there is a very comprehensive thread regarding this on FABO right now. go to "brakes" and in the brake drum source sticky at the top I posted the math on how to mark out a template which is the same thing a machine shop is going to do for you (at an hourly rate). You need to be straight on the shoe width/drum width/b plate offset combo you want to use for fitment and the larger center "register" hole diff between SBP and BBP needs to be dealt with. EDIT its the "B body rear brakes onto A body axle" thread