I just got my 1992 IROC R/T back together with a lot of new parts. I think their may be multiple issue here but I was looking for someone with experience on this. I just rebuilt a new to me A523 with an OBX. Any time I step on the accelerator I can feel a pretty strong vibration, but only when accelerating.

I just installed the Rich Bryant BC Racing Coil over suspension on the front. I think the front is still too low as the lower control arms are pointing up instead of level or down. I have not gotten an alignment yet, so I have no idea how far that is off. I am going to add another 15mm of height in the front and see what that does. I have not had a chance to install the rear set-up yet.

On the motor mount side of things, I already had a Polybushings front and driver mount installed. I added a Polybushings passenger mount. I have a solid bobble strut. After installing the engine with the passenger and drivers mounts, I installed the front mount. I then added about 1/8" of preload to the bobble strut.
I literally took the car for a 15 min shakedown this morning just to see what is going on.
I need to raise the front as said and also get an alignment done soon. I am not sure if this vibration is caused by binding because of the front being too low or this vibration is being transferred because the motor mounts.