Summit is not the only place selling .500 dowels for Mopars, Jegs, Speedway and a bunch of others including Mancini. The picture below might explain why.

After evaluating things a bit further and talking with the owner I am going to relocate the ball stud on the BH bracket unless Someone chimes in with a solution. The owner is running out of $$ and I am already buried in this. Not the solution I would prefer but an easily reversible one at a later time.
I will update once the car is drivable
thanks to all that have contributed

Loosened up the motor mount bracket bolts that attach it to the block, leave them slightly loose.

Raise the engine then tighten the bracket bolts. Leave the motor mount to k frame nuts loose slightly and raise the insulator too. This may get you what you need.

Thanks , I am aware of how they are listed and found out the hard way in 2005 that they are not right when I was helping a friend use a set of the Lakewoods to dial in an Ultrabell on his Challenger dragcar ... what a nightmare

What rubber engine mount is he using on the driver side ? I went thru this with my dart , the replacement mount I got , think it was schumacher , is thinner than the factory mount , I replaced my worn oil soaked original mount that was crushed and sagging badly , I bought the shims that Schumacher sells to level what I have . I think what they were selling was a mount that was not the actual for the application , also their poly ... if I remember right ... is also thinner than stock which is why they have the shims . I scored an NOS original mount that i haven't dared to use as of yet , shimmed the left replacement to get the engine level.

To me, the engine & trans have to be level side/side.
I'd be loosening the mounts & brackets, and with a carb plate or whatever, correct that.
Could be an incorrect mount, damage, or sloppy fitment.
Mission creep can suck, but better to have it right than not.
Might have to watch header fit, and hopefully more things weren't "rigged" to accommodate the leaning.

I made the D/A mistake of doing the Block side of the dowel but not the BH side. When I installed the BH it was snug but not overly so.
When I figured out I had put the fricken pins in 180 out the R pin had been pushed into the block and seized. NIGHTMARE is an UNDERSTATEMENT

To remove a siezed dowel. Weld an allen bolt (hex side) to the dowel. Slide a socket or piece of tube over the allen threads. Install a thick washer a little anti sieze on the threads and yhen a nut. Tighten the nut, it'll pull it right out.
Doug

To John RR as well: The mount appear to be an original and in excellent condition (surprisingly). Maybe it was replaced when the car was restored 30 or so years ago

I did consider shimming the L side but there would still be a front to back angularity issue (yaw). In addition the poorly made L head pipe will the be too close to the torsion bar ( has already been clearanced once). There may be a few "other" issues that arise as well
I am already BURIED in the car time wise and the owner is starting to squeal.
So, with all considered I think the kwik and dirty is to mod the BH mount and deal with it at a later time. No permanent change or damage done to the car and it can be easily rectified when he has more $$
I again sincerely appreciate the input and help, will keep all posted

Have you tried loosening the bolts from the engine brackets to the block on both sides and leveling it that way, tighten once level ?

I'm not sure I'd get worked up about the Z var not being level. It is supposed to be able to cock a bit to accommodate engine rock under load.

As long as it's not binding, I'd let it go.

The Z-bar has small nylon bushings @ each end which can fall out if the Z-bar torques too much.
Suggest making sure the motor mounts don't have excessive end-play, and install a torque strap.

Just my $0.02...

I have not as I have to draw the line somewhere. If it were my car it would be a different story but he's starting to squeal and I'm buried in the car time wise . I have been down this road MANY times and have finally realized at 69 YO I can't fix everyone else's problems, especially for free. I have a very tolerant patient wife that has been neglected way too long.
Had a guy Call yesterday while I'm in the middle of an important phone call. ( the website clearly states to call ahead and make an appointment). Did he ? No. So I spent way more time than should have talking with him and giving him suggestions on things to try. Also referred him to another shop.
10 minutes after he leaves he calls and said it quit again and won't start. Well it quit 3 times on the way here which is about 20 miles away (there was a clue there). So am I supposed to drop everything and go bail this guy out? Sorry, told him to call a flatbed. I am done being taken advantage of and being Mr. Nice guy. I've seen very few people offering to help FOR FREE when I've needed it. Sorry for the RANT but I'm DONE!!! I love the work and I like helping others but I can't fix everyone else's problems.
I do want to Thank you for the suggestion(s) help and all the effort you have put in helping others on this site, myself included NUFF said

it's close to binding both laterally front to back and horizontally. The car has been this way for as long as he's owned it and I've made note of it before. The reason I have tried to correct it is I had it apart for the clutch issue. As mentioned, I'm in to deep so I'll do the best I can for free. The root cause will have to be addressed at another time. thanks for the input

Any stick car should have a torque strap(we’ll probably most autos too) because once you feel how much easier they shift you’ll wonder why it wasn’t on the option sheet back in the day.

I also agree and every stick car I've owned had had one at the front and back of the motor. The back of the motor came about as we were losing transmission mounts after trips to the strip back in the day. We were on slicks with the suspensions set up so that may have been a factor

You don’t need a torq strap if you use solid engine mounts. Ride quality on the street will suffer a bit though. I currently run Mighty mounts with an adjustable torq strap and OE tranny mount. I tighten the strap when I race.

The problem I have with solid motor mounts is the noise and vibrations through the chassis...
My preference is to use a adjustable torque strap, adjust it closely to take up any slack the engine/drivetrain for the drag races and back it off when street cruising ...

Just my $0.02...

I think there is WAY WAY too much time trying to make the linkage "perfect" when that is not the cause of the chatter issue at all. I have seen some really misaligned linkage before work perfectly my car included. It's inside the bellhousing, the flywheel, the plate or the disc is the issue here. Get the flywheel surfaced by a good machine shop then make sure the disc is not warped with a dial indicator and some type of lathe and a dial indicator.

As for solid motor mounts or motor plate if your stuff is balanced right there will be no severe vibration issues. Mine is smooth and I have gotten compliments on how smooth and quiet it is. Been running a motor plate and a poly transmission mount since I built my car about 30 years ago. The only clutch that chattered for me was a Ram sintered bronze 6 puck disc and a Hays race adjustable plate.

You have to start measuring from the crank flange then the flywheel to make sure you don't stack tolerances. Something is warped or bent somewhere.

Gus

I agree with all this except the tranny mount. None of what had been mentioned here will cause chatter. Dirty flywheel, pressure plate or type of disc material could and will cause chatter. One end of the z bar holds the nylon bearings in place. The other side slides free to compensate for engine torq. This doesn’t have to be perfect. That’s what the nylon bearings and the ball fittings compensate for. The other stuff mentioned will certainly help with drivability, but not cause chatter. Gus and I have been doing this for many years. Lots of experience between us. Just sayin’.