Not exactly a bolt in per say, but you can use a rear from a 64-72 GM A-body(Chevelle,GTO,GS). You will have to use one of the arm kits from HP Motorsports or the Southside kit. You will have to relocate the spring and shock mounts by welding new parts to the housing which doesn't make this the bolt on part of the swap. Downside is these older rears have longer tubes so you will have to change the backspacing on your wheels too. I have the 8.50 rear from a 72 Skylark under my GN and from a cost perspective I would say the total package with wheels and everything is only slightly cheaper than an aftermarket 9" Ford or GM 12-bolt.