The neoprene seal made its first appearance for the 1956 model line. At least the pass cars. So you can find a block cast as early as late August 55 that has the rear cap machined for the new seal. What I have not been able to determine with any kind of confidence is whether the truck blocks, 56-63 came with the neoprene seal or came with rope seals. I ave seen them both ways but never a truck block that had not been rebuilt so I don’t know one way or another for certain. I have seen 57 and up blocks with the rope seal. For a while that neoprene seal was really hard to come by. The original seals were an asbestos based seal, new are fiberglass graphite affair and don’t really work all that well. If you have a 57 block, hold out for the neoprene seal. It will still mark its spot, just not as bad, lol!
