Maybe this will help.....or at least I hope it will
This is a from an engine blueprinting book published by SA Design:
"In 1986, Chevrolet small-blck V-8s began to use a one-piece rear main seal and matching rear main cap in an effort to stop rear seal oil leaks. This required changing the rear crank journal, flywheel, and flexplate bolt pattern diameters, the oil pans, pan gaskets, and timing chain covers. Similar changes were made to chevy Gen. V and Gen VI 366, 427, 454, and 502 big-blocks in 1991 and 1996, respectively. Chevrolet and some aftermarket companies make rear seal adaptors that allow the use of early two-piece rear cranks in late model one-piece rear main seal block. Depending on which adaptor you choose, an oil pan designed for a one-piece or two-piece block cn be used. The rear seal adaptors are helpful if you have an expensive crank made for a two-piece seal and wish to use it in a one-piece seal-style block. The adaptors come with the required bolts, dowels, gaskets, and instructions concerning the drilling and tapping of holes to mount the oil seal adaptor."
Their mainly talking of using an early model crank in an late gen block, but it should have the information your looking for.
