Yup, what he said for the most part. SBP refers to the 5x4” pattern, BBP refers to the 5x4.5” bolt pattern.
The year split is a little less clear cut. ‘63 to ‘72 all production A-bodies were SBP, both disks and drums.
In ‘73, all of the front disk brake A-bodies went BBP. But cars that had front wheel drums stayed SBP. All of the V8’s got disks, so, SBP was just /6 cars. And some option packages upgraded the /6 cars to disks. In ‘76 they all went disk and the SBP went away.
To add more confusion, in ‘73 the upper control arms changed as well to use the larger ball joint already used on all the other models. Even the 10” SBP drum cars got the large ball joints, so the 73+ drum spindles are different. They also had larger wheel bearings than the earlier drum cars.
