It might seem like a silly question for some of you, I have a 69 327 with a 386 casting. If this is the same casting # as early dz & 350 engines, why do 302 & 350 use different motor frame mounts than the 327 ?
One of the first and largest auto recalls back in the '60s was caused by failure of the LH motor mount in 8 cylinder '65-'68 Chevrolet passenger cars. When the mount failed, under acceleration the engine would lift off the bracket, often causing the accelerator linkage to bind. The car would continue accelerating even after releasing pressure on the fuel pedal.This caused several serious accidents. The recall involved the band-aid fix of a cable/bracket assembly attached to the exhaust manifold and looped around the upper control arm shaft.
For '69 Chevy re-designed the mount with an integral hook to prevent physical separation of the parts if the rubber/metal bond failed. The "interlock" mount was narrower and thicker than the previous design necessitating re-designed frame brackets. For sb '69 Camaros Chevy only used the new mount/brackets with 302 and 350 engines, deemed most likely to need them. 307 and 327 engines continued to use the old design.
The problem with this is the early mount will fit the later interlock frame bracket. It is a very sloppy fit; the engine will be positioned too low and can easily move around causing clutch chatter and driveline vibration.