Not going to do what I first posted bad idea just thinking out loud. Vibration 27-2800 rpm and up.

Are you talking about leaving the clutch disc and pressure plate loose on the input shaft with the motor running? If so please don't

That is a REALLY bad idea. Please describe when, how you're getting a vibration. If you have eliminated ALL other possibilities (there are many), and you are down to JUST the engine as a whole and the pressure plate, then drop the transmission & take the flywheel and pressure plate to a shop that does balancing. Have a shop balance both separately & tell you how much they had to add/delete from each.

Your problem might be as simple as a harmonic balancer....7 bolts & done.

Could be as simple as the pilot bushing missing

I'm trying to push it back to the engine builder. It starts at about 3000 rpm in neutral or in any gear and standing still. Engine was complete with fly wheel and pilot bushing I added the clutch, trans and drive line.

Is it vibrating at 3K and anywhere above? Or just around 3K? Just common sense thinking here, if the engine were that far out of balance then the vibration would be worse at idle. Sounds more like the clutch is stupid out of balance. Could also be bell housing misalignment.

If you want to check engine only, need to pull the transmission, support the engine and fire it up. Agree do not try to run it with clutch loose.

In the spirit easy things first, what about the damper (balancer)? SB and BB sometimes use a counterweight damper and sometimes not. Plus there are different amounts of imbalance used depending on how the engine is set up. If the vibration damper is not matched that could cause this problem.

Pilot bushing does sound like a possibility....or motor mount.... or 1/2-dozen other things. I know you are probably pissed, but take a moment and breathe.

a. Check all the easy stuff & just deal with it. Priority #1 is to drive the car, right? Balancer, motor mounts, transmission mount, one plug wired popped off, bad plug, cracked distributor cap, other?

b. phase #2 is pull the transmission. You cannot push it back on the engine builder unless you have absolute proof that you did everything 100% correct yourself. Pilot bushing/bearing, pressure plate balance, transmission bearings/bushings, etc.

It is a brand new restoration so everything is fresh. I'm going to have it on the ground today for a better drive. When I first fired it and at break in 2000 RPM all is good but then I revved it a bit higher and it shook. I figured I'd put it off and finish the car and address issues after completion. I took it around the block from the alignment shop to my trailer and was not pleased to say the least. I was skeptical about the engine when it arrived all the screw in block plugs water and oil were loose and a nut laying in the valley pan, not how I do things. I needed to step back blow some steam and get after it, I'm sure I'll get stuck finding the problem anyway.

You might be chasing a ghost?, confirm some basics first, good sparkplugs?, firing order truly confirmed?, if running vacuum advance make sure the advance arm/pin didn't fall out of the dist's plate/pin hole?, PCV valve OK?

I had vibration problems on a new motor install also. Turned out to be the Centerforce DF clutch that I added. I pulled the transmission, removed the clutch and fired the motor. Was smooth as silk confirming that it was the Centerforce. Just a thought if you went that brand.

I have all my flywheels and clutch pressure plates balanced with the crankshaft assembly on any stick shift motors I build
That being said look very closely at your flywheel and pressure plate to see if there are any balancing holes in the flywheel and any weights welded onto the pressure plate
Is your motor a BB or SB?
What size clutch and flywheel?
Is there any big holes drilled or machined into the engine side of the flywheel? If so that flywheel was intended to be used on a external balanced Mopar motor

Yeah, I'm with Dayclona on this one....might just have a spark plug wire fall off. And I hate to say it, but just about every tine I've rebuilt/installed a motor, there was "something" I missed...often 2 or 3 things....forget to tighten a hose clamp completely, not hook up the field wires on the alternator..."something"....you will get there brother, don't worry. Try the easy stuff first.

Took it for a good drive. It shakes the car moving or not from about 27-2800 RPM all the way up, getting to warm out to mess with it so until tomorrow I will get on the basics. This and a good detail and its ready to deliver.

I have the same problem with my centerforce dual friction. My weights get stuck off center once in awhile and i have to reach in and push em around.

bet Ray or the Oil Baron would know

Fixed. Damper balanced by said machine shop, I had one for another project the shakes are gone.

Wow! Who woulda thunk? Glad you got it fixed much easier than pulling the trans.!!!