[70GMCer]

1967 thru mid year 70 requires 1/2" spacing behind the backing plates & also you must use the late 70 thru 72 brakes & drums. Check the build date on your rear, (man, that sounds personnel), to see if you have the wider one. The wider ones are 3/4" longer than the late 70's. This is assuming that you still have the original 12 bolt rear on the truck. This is what I've read on here a while back. I'm still thinking on doing the swap myself......