Hey yall, just signed up to do some research about B body wheelbase differences and it seems I found some happy news.
I've got a 69 RR with some poorly repaired collision damage from way back and lots of pinholes in the floors and rails. I just picked up a very rust free 68 Coronet 4 dr to use as a donor and was expecting to have to shorten the floor pans and maybe move the rear rails forward.

But this sounds like I should be good to go with stripping the Cnet down to the floorpan and grafting on the RR roof/quarters. Still a lot of work but I can keep the pan assembled (therefore square and level)
So just to confirm: the spring hangers (bolt on brakets) account for the longer wheelbase and maybe the shackle mounts are different?