Engine Vibration Trans Am 1977

This vehicle with 75,000 Miles and never winter driven. Vibrations began after test run when clutch was replaced. The acceleration was great and no vibrations hrs after the clutch change, but with the peeling of the wheels and high acceleration during test run to see max performance turned sour. Soon after a 2 mile test run vibrations from engine began and after years of shop repairs, no solution to this problem. Here is a list of repairs over the years, but still not fixed. Note the vibration is present even in park position, noticed by the side mirrors and the body.

The engine mounts replaced twice.
The drive shaft replace with new joints.
The Clutch, plates and bearing replaced twice.
The flywheel mechine and balance each time.
The compression test done as passed with cylinders O.K.
The harmonic balancer checked O.K.

I was told the last option is to change the chassis mounts and flywheel.

Can anyone help? I am anxiously awaiting any idea..........

Thanks,

Heavy vibration indicates somthing wrong with the engine internally,usually having to do with the cam,valves or lifters.reset your rockers,and put a fresh tuneup in it.A lot of people get new motor mounts,and since they are newer and not worn out,they tend to distribute more vibration to the body than a worn engine mount .If your using high performance engine or tranny mounts,or factory steel mounts,they always add some vibration.You might have damaged the cam or bent a pushrod or valve during a burnout.I say that because while a car is spinning the tires,is when its easiest to over rev the engine.

Thanks for the input. I have already replaced the valve seals but no checks so far to verify the cam and valves etc.

Any hints, as I need to check with the mechanic....