Re: bad engine/ transmissiom?? vibration
Well, it sounds like the vibration just started, and after you did some WOT running. So I gotta think you damaged something or something just loosened up.
Check obvious stuff, like vacuum hoses. Maybe something in air cleaner is now obstructing carb (if you've got cowl setup, then air cleaner may be hitting). Broken engine mount could have let the engine raise up and bend/break something.
Maybe a plug wire fell off, or a spark plug just went bad, so now you've got one dead cylinder.
I would say, check basic tune-up items first. Then compression check. Then check tranny for loose or cracked flex plate. Also check engine and tranny mounts.
Might have jumped a tooth on the timing chain, assuming it's got a lot of miles on it..............
Dave F. in Rhode Island
'68 Camaro SS Accel DFI 454 (SOLD - I'm a boring Corvette owner now)
Bought my first big-block Chevy in 1970