The simplest, and least expensive option is to grind divots into the block webs to use the late 55-61 main bearings. Every other dimension is the same- - - -inside and outside diameter, width, oil hole placement, thrust bearing width, etc. Even the lower bearing shells have the same dowels included. The only reason for the upper bearing modification is to make it easier to change main bearings with the crankshaft in the engine. Make about 2 more posts and you'll have access to the private message option.
Jerry
