Thank's for all the replies to my OP.
I think I knew the answer all along.
I guess I was just hoping someone would dissuade me from the obvious
As for the rear bracket.
When I first put it together, it just seemed the right thing to do.
I put on the Sierra rear bracket, and it fell right into place of RS6.
So I bolted up a plate to the diff bracket, and welded it in place.