Need advice about solid mounting a 340

Even if you are running a transmission mount you still MUST use engine limiters. Preferably one on each side of the engine. Otherwise, the engine WILL actually scoot down the tunnel when you drop the hammer.

Well technically, the engine stays where it is and the chassis moves forward into the engine but the end result is still the same.

It's like saying when you romp on the throttle you get set back into your seat. That's not true. The seat is actually ramming into you.