FWIW the 1955 2nd engine I have has main bearings pinned top and bottom and a low water pump. When I rebuilt it in 1973 I used the rope seal in the gasket kit. I don't recall whether there was a neoprine one. Anyhow the engine turned nicely till I installed the rope seal. Then it wouldn't budge without a large screwdriver on the flywheel that I had installed to get it to turn over. As I recall, it took a great deal of persuasion with a hammer and a piece of wooden closet rod to beat the rope into submission. I think I soaked it in oil and squeezed it in a vice to make a shape that would fit into the groove. It didn't leak for many years after that but eventually it did and I tried the one piece neoprine seal that was available at the time. It leaked. Not much but some. Later I changed clutches and main bearings and the seal, this time with the two piece neoprine seal. It leaks worse. Not a lot but enough to be annoying.
