On my 69 with its original 351W block, I really had to wiggle and convince the motor mounts to drop on to the tabs. Fender aprons and towers are untouched and in perfect shape. The car has never been hit and the frame is straight as an arrow. With the fan and fan shroud on, the engine sits about 1" or 1 1/2" higher than it should. Can motor mount quality be the difference?