Dave/Venture,
I am not sure on this, but I remember the rear main seal surface on these engines being separated from the main bearing journal area by a slinger that was part of the crank. The seal surface was very narrow...too narrow for a crank grinder! When a crank was ground, this seal area wasn't touched. I don't understand how a neoprene seal (top half) could be installed with the crank in the engine. I have done several rope seal installs with the crank in the engine ( loosen all mains and drop as much as possible) using the chinese finger trap. This requires lots of slick-um, rolling of the crank and later, precise trimming of the ends. Seals will seal when properly insalled, so keep at it.
Stuart.
