i am rebuilding a motor too, and thanks to your post i rechecked my side clearances on my 3/4 rods cuz they were a little tight, and will be fixing that.
I used plastigage on all my bearings and every one came up tight. like one and half thous. i took the crank and the torqued rods with bearings in them to a machine shop and they verified i actually have 26thous. perfect! they also told me my crank had been turned to the low limit, which i was told, but they did verify it.

I don't like plastigauge or snap gauges, taking the parts to a machine shop was the right move.
On clearances
: if the clearances are a little loose, only you will know. If they are too tight, everybody will know!

You can buy your own stuff and measure it yourself instead of paying somebody. Good, used measuring tools are all over ebay. If that type of precision is beyond you, maybe you should just let someone screw it together. Not bashing, just being practical. Blowing stuff up is expensive.

see if you can get a dial bore gauge to check the i.d of the rod bearing. I've never had a warm fuzzy feeling using snap gauges for precision measuring and usually just throw plasti-gauge away.

I find plasigauge is good to measure taper but tends to measure a touch tight. Maybe because the other side of the journal isn't pulled tight to the crank? I think you'll be fine.
Doug

No kidding, I'd rather have 6 than 2. .0035 is my norm until it's going over 2,000, then .004 or more.

I've never once seen wide hurt anything, ever. I've seen tight destroy everything.

Even saw a motor that was raced all season on spray with a .010 under crank and standard bearings (.013 clearance) never missed a lick. Made about 1500hp on spray. Idle oil pressure was about 20 cold, and 5 hot. Would climb to about 50 psi on a 7500rpm run. No damage to anything.

on both subjects
I've used gauges and plastiguage, once only on the plastigauge
On using a inside mike compared to a snap gauge the individuals feel can be the difference between .0020 and .0023
I've bought three different dial bore gauges( .0010, .00050 and one .00010 accuracy) and finally realized that setting them up is the key to a decent, accurate reading
If the gauge is marking a line in the bearing is it removing material or not Does that mark really matter
As far as this old post goes, it would be interesting to hear how much clearances the OP ended up with and how those clearance have worked
I'm like a lot of the other posters on this subject, a lot looser( 0.0010) is way better than a tiny bit (.00010) to tight

I'm a retired tool-maker, any measuring too you use is only as good as the user. snap gauges (telescope gauge) is as accurate as an inside mike. Its just how you use them. Once you pull it through, don't do it again. Measure it and you're done. On any inside measureing tool its a good idea to put some light oil on the contact ends. Dial bores will always leave lines on bearings. A little oil will help a lot. The set up on dial bore gauges is very critical . If you don't have a ring gauge you can put your mike lightly in a vise lock the barrel on your mike to the size you want have the mike in vertical position. With the solid end of your dial gauge down on the center of the mike anvil. lightly swivel the plunger around on the top anvil and set it at your smallest reading. If you have Jo blocks its much easier and most accurate. Hope this is of some help. Good luck

You could have the crank polished down a bit, but 0.002" should be fine.

I would not do this. Sorry to disagree but polishing it does not guarantee it will still be round when the guy is finished. As a matter of fact, I can almost guarantee it won’t be round. Several years ago, my machine shop sold out to a new guy and he had never run a crank grinder at this shop. He could do everything else very well. So I had to go elsewhere for one crank. That guy made so many mistakes on that crank he ruin it. Over polishing was one of them. It was .0005 out of round plus it had a taper on the end of each journal. Terrible job, it was. I caught it with plastiguage. I hardly ever use it. I found different brands of snap gauges will measure differently. I use Starrets before I got my dial bore guage. The snap gauges measure slightly bigger than a dial bore guage IMO. Maybe .0002. But as said before, it’s mostly in how you mic or feel the mic. After saying that, I think you’ll be fine with that. Now you could do what I do. I have the cranked turned FIRST. Then if I need some more clearance, I size the rods to the correct clearance. This works best for my shop.

There is a rule of thumb for clearance... its something
like .001 per every inch of diameter
Industry standard for 100 years.
If you decide to run .002", use a light value for the oil grade first number: 5W, not 20W.

as a retired machinist, the above is spot on.

I buy a lot from them, saved almost $400 on my rods vs what Summit and Jegs listed. They also ship fast.

Big clearances with light oil. You can't be squeamish about oil pressure if you go down that path. Especially at hot idle. You may as well take that 30# transducer for the light and throw it in the trash. Put a 15# in it and put up with the light flickering at you coming back the return road.

I use the old ten lbs. per thousand RPM rule with hot oil, 10 lbs. at 1000 RPM, 65 lbs. at 6500 RPM with 5W20 weight oil

I agree. Use a good oil pump and run a lot of clearance.

I built 2 408 with .002" rod and crank oil clearance and never had a failure with that at 7000rpm. Bearings had odd markings but never burned to copper on rebuilds. Street/strip deal. Local circle track engine builder builds all his sb chevys that way. I would never do that again thou. Always better to have .0025-.003" on rod and .003+ on mains. I have my 511 at .003 on rods and mains. I sleep better with it that way.

W/r/t using sequential sizes, such as one +.001" and the other +.002" to get the intermediate +.0015" total where desired (Ford factory manuals for the “Indy” 255, “Le Mans” 427, and “Trans Am” Boss 302 recommend this): the larger oversize (looser clearance) is generally the upper rod bearing half, and the lower main bearing half.