[Sirrotica]

Anyone that is contemplating solid motor mounts needs to look at a picture of a Pontiac block upside down to see that the 2 bolt motor mount location transmits all the twisting force to only one of the main bulkheads, #3. By looking at the early 2 bolt mount location, and the added strength of the later 3 bolt mount system it's obvious why Pontiac engineers redesigned the mounting system for higher torque applications with the advent of the 455 in 1970.

It's been determined in some instances to cause the failure of the cast iron on this location on stock blocks. Pontiac redesigned their mount system on the latter 455 applications to 3 mounting points and using #2 and #3 bulkheads for superior strength.

I personally have used a engine restraint system since the mid 70s, consisting of a turn buckle attached to the left cylinder head and the frame, and still use the OEM mounts successfully in conjunction with the restraining link. This completely removes the stress to only the #3 main bulkhead area. It makes me sleep better at night with the improved system of restraining the engine.