Same casting - 2 bolt main variant as opposed to the 4 bolt main used for the higher hp engines. What always boggled my mind about this is that building both 2 bolt and 4 bolt engines out of the same block had to have created additional part and inventory control issues for Chevrolet / GM with regard to usage. One would have thought the block would have been machined the same for all builds (302, 327, or 350 usage) and simply change the internals as required to build the correct displacement. But they didn't. Although one could argue additional machining time to bore and drill the extra holes, this doesn't make sense to me either in that I suspect that all of those drill and tapping machining steps were all automated and done at the same time. However, someone had to keep up with and make sure that the 2 bolt main blocks went where they were supposed to go and likewise for the 4 bolt main blocks. Had to be some additional manual labor hours there.
The 327 in my '69 RS is a 386 block, assembled at the Flint engine plant on 11/22/68. It is a 2 bolt main block - as were all 327 engines built by Chevy.