Here is my conclusion. . .I have decided that I likely have a clutch disc problem, likely contamination from a leaky RMS.

I think the reason it reared it's head after I changed from early tranny mounts to late, is that the duel early mounts are much more solid. Clutch chatter is really the drivetrain bouncing in its mounts from the clutch grabbing (meaning a car with solid mounts wouldn't exhibit "chatter," even with a sketchy clutch) and because the single center mount is much softer, it seems to be more sensitive to a clutch that doesn't engage smoothly.

So, after laying on my back for a kazillion hours converting the fuel tank and crossmember, looks like the drivetrain will be coming back out to inspect the clutch. On the positive side, I think the shop time of 10+ hours is a bit high. . .we'll do it quicker.

Thanks everyone for your help. . .I'll post results back here when I have it done.

OK im scared now...
I just replaced my clutch and this happened after i got my car back.
I havent returned it to have it looked at bc i just got it back parked it and went out of town.

my motor mounts are new, axles are new, clutch is new, flywheel was resurfaced.
i dont think an exhaust hanger can cause as much vibration/wheel hop/shudder as it is doing from 3-2 only.