around '55 or earlier you should stay with the rope seal. the factory machine work in this area left alot to be desired & the neoprene seal often times won't seal. on the later engines the neoprene seal works well, most of the time. contact becks machine ( there's a link on this site ) if you have problems. they have a way of machining the block & bearing cap for a full circle seal. they'll even tell you how to get it done at a shop in your locale. hope this helps.
robert.
