I have seen stock mounts fail with just normal street abuse at stock power levels.
I asked you about this in the thread you had started about your valve springs & push rods.
Stock motor mounts or Solid mounts? Yes or No ?
Torque strap on engine to frame? Yes or No ?
If you are running stock low durometer rubber mounts the rubber one on the compression side is going to eventually pancake .
The one on the tension side will try to lift and separate.
You might want to look into "Mighty Mount".
The transmission mount should be rigid or stock style w/ solid urethane pad instead of the stock rubber mount.
You want to eliminate as much drive train flexing and binding in the frame as possible.
Step Away From The KOOL AID !