I bought a VE valiant years ago that had been raced quite a bit through its life, along with being street driven. I think it was a B/Street car back in the day. Anyway, whomever built the car, took a pair of the factory rubber isolators and welded some steel plates to the sides to make them solid. No idea how long they were in there for, but it looked like a while. Might be an option to try if you've got some mounts lying around.

I didn't notice the engines mounts causing vibration, the rear ladder bar set up this car had made enough noise and vibration, I didn't notice.