340 8 bolt crank info wanted

I have pin pointed it to the rotating parts- flywheel, clutch, crank, engine internals. It's not the trans or driveline, does it in neutral sitting in the driveway. Ruled out ignition, misfiring, pulleys, external accessories, etc. I replaced the harmonic damper with a Fuidampr hoping that would fix it, but no difference at all so it's not torsional vibration.

I didn't build the engine. It's supposed to be about 382 cubic inches with 4.064 bore and the stroker crank and if that's accurate then the stroke must be 3.74". Don't know what rods are in it, but it has J&E pistons. I was told it was balanced when built. I've got pics of it during the build and it looks like a quality job so I have to think it's balanced properly. Tons of power but I can't use it since it has this vibration that shouldn't be there.

Next step is to remove trans and pressure plate/clutch and run it and see if that fixes it. It's a new McLeod billet flywheel, new clutch, new pressure plate for internal balance engines. I did not have them balanced, probably a mistake but I've never had to do that on any 340 before. McLeod recommends balancing them (wish I had known that) but I really doubt they are off very far. This vibration is bad enough that when you get on it it makes you want to back off before anything comes apart. Starts above 1500 rpm and never goes away, doesn't reach a peak either. Feels like something out of balance.