The cast iron PG bolted to the block with an adaptor flange. The bell housing bolt pattern on the 283 was not different. As I recall, the adaptor flange had mounts that supported the weight of the rear of the engine and the transmission. There were no side motor mounts on the blocks cast in the early years. Of course, the iron PG was very heavy and needed the support since the front was mounted using a "foot" that bolted to the four 3/8" holes just above the pan rail, two on either side of the harmonic damper.