Once you get the main bearing cap removed where you can inspect the sealing surface of the crankshaft, check for grooves or rough spots. If the surface isn't smooth, any seal you install is going to get torn up in a very short time. Neoprene seals in particular are subject to damage from a rough crankshaft surface. National Seals, SKF, and a few other companies make a 3 7/8" Speedy-Sleeve that can be installed on a stovebolt crankshaft, but the shaft would probably need to be out of the engine to get a good installation.
Jerry
