Small bolt pattern axles (5x4") use a different axle flange offset than big bolt pattern axles (5x4.5"). The difference can bee seen here
View attachment 1715363247
That difference in flange offset is REALLY important. It means that none of the drum brakes used for SBP axles can be interchanged with the drum brakes used on BBP axles. The backing plates are different, the drums are different- not just the bolt pattern.
So, if you have your SBP axles re-drilled for the 5x4.5" bolt pattern, you still have to use SBP drums and have them re-drilled as well.
The problem really comes in with some of the aftermarket axles. Unfortunately, there are aftermarket axles that are made with the 5x4.5" bolt pattern, but the small bolt pattern axle flange offset. Which is terrible, because you can't just look at them and see they've been redrilled. But just like a re-drilled axle, those 5x4.5" bolt pattern axles with the smaller flange offset MUST use SBP brakes with the drums re-drilled for 5x4.5".
If your new axles are BBP and have the BBP flange offset, then any 10x2.5" drum brake set up will work for you. They came on RWD cars as late as '89, and are pretty easy to find. But you need to use the entire set up, backing plates, shoes, drums, all of it. And those drums are readily available.
If your new axles are 5x4.5" but have the SBP flange offset, you have to re-use your old backing plates and have the drums re-drilled, and only SBP drums will ever work for you after they've been re-drilled.
