Hy Achipmunk, that block was used for any 4" bore application 302, 327, and 350, it is a post 1968 block [large crankshaft bearings], and I've seen them in both two bolt, and four bolt main configuration. I don't know when they stopped using the number, but 1985 would be the newest [1986 was the first year for the one piece rear main seal I believe], hope that helps some.
