Ott3R, are you 100% certain that your block is a 56? The reason that i ask is that the rear main cap was machined differently from 55 to 56 because 56 was the first year for a neoprene rear rear main seal. The 55 main caps are machined deeper to accommodate the rope style seal. The 56 and later blocks were specifically machined for the seal. The difference is why you cannot retro fit a 55 and earlier block with a 56 and later neoprene seal. So if you have a 56 block, you might consider using the neoprene seal. There was a reason that GM moved to that style seal as opposed to the older rope style seal.
Last edited by Dragsix; 04/06/2020 7:17 PM.
