What are pitfalls of "hard mounting " tranny vs rubber mounts?

its a 3 point mount: 2 motors and a trans. If you hard mount any without a pivot, your going to get cracks from torque flex unless you control it (3 hards or a torque strap) Using 2 flex on the motor and 1 hard point on the AL trans will end up cracking it back there. How about motor isolators on the mount where it attaches to the frame? So the whole yoke is isolated?
I am using one of Dennys HDK tubular K frames so I would consider the motor hard mounted? Plus I am using sub frame connectors? So in theory I actually need to hard mount it? Thanks a million guys.