Buddy Neely put a set of the 3 inch ID Powerstick mufflers on his Backdraft. He got the mufflers from Classic Chambered Exhaust, Inc
http://www.classicchambered.com/classic/products.html
He also got the 3 1/2 inch turn outs. We cut the old mufflers at the front of the muffler and welded in the new Power Sticks along with the 3 1/2 inch turn outs. We also welded in some O2 bungs while we were at it so we could hook up an Innovate LM-1 for tuning. As for the rear end in your Backdraft, I don't know if the BMW rear end will handle the increased horsepower along with slicks/drag radials. We took the BMW rear end out of Buddy's Backdraft and put in a 9 inch Ford rear end with a triangulated four link and QA1 coil-overs.