BOP short tails are going to be from 67-72 A-body 2 and 4drs (wagons have a long tail), 67-70 Riviera, 67-70 Buick Fullsized, 67-76 Firebirds with the 400/455, and for whatever reason the 74-76 Pontiac Grand Prix. Best core would be the BB code from the 70-71 Buick GS455 or just about any TH400 from after 1969 as they changed the internals and the filter to the more common stuff. My '64 ST400 is a 1 year weirdy VB and takes the "submarine" filter verus the newer "pancake" filter you can actually get.