Small Block Blocks General Info :: 1964 - 1990
4 Bolt Mains
Except for experimental and ultra-exotic [Mondello, Dave Smith Engineering, etc.] custom setups, there is no such thing as an Olds 4-bolt block or main caps [455 or 350, etc.]. There were never any made.
Oversize Lifter Bore
With any block, watch out for the 'O' stamp on the lifter bore boss, indicating a 0.010" oversize lifter. Either Oldsmobile would only have stock 0.010" over replacements or THERE ARE NONE AVAILABLE. Which means you either get to sleeve the lifter bore (difficult and expen$ive), or scrap the block, or, re-use that old lifter. Resleeving the lifter bore is not fun.