Re: Slotted holes on GM engine mounts??
IMHO, I wouldn't worry about it. From the pictures, it looks like you are talking about the part that bolts to the frame stands. The frame stands would have to be slotted also, for the engine to move (if the bolt is tight). There is more movement in the rubber (or poly) mount. Make sure you are using Big Block stands, which will offset the motor.
69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1