84 monte G-body, I need help with a 12 bolt swap, and rear wheel/tire fitment.

[fonz3482]

Hello everyone,
Some day soon I plan on starting my 84 monte build. My dad has given me a 12 bolt posi rear end out of a 72 pontaic gto. It has 4.11 gears and was in great working order when he pulled it from his car many moons ago. My questions are- I know the 12 bolt is wider than the stock g-body 7.5", but how much wider is it? What rear wheel backspacing will I need to keep the tires tucked under the car. Also What tires can I run without a frame notch?, and what can I run with the frame notch? I currently have 15" wheels with new tires on them, so I may keep the 15" tires and buy new wheels to save money, Or if I have to buy all new wheels and tires, I'd probably go to 17" tires and wheels. Any advice, or info would be greatly apprecaited. Thanks

[Tony_SS]

I would put it in and put your old wheels/tires on there and use that as your guide.

I had a 12 bolt in my old 84 SS, but I don't know what year it was from. The wheels stuck out some, 15x8 with 295 tires. :)

https://static1.pt-content.com/images/pt/2012/07/81c-1.jpg

https://static1.pt-content.com/images/pt/2012/07/cae-1.jpg

[Brokenmonte1987]

Aaaaay Fonze ...I had to do it.
I have a 12 bolt from a 66' chevelle in my 87 Monte SS, using the stock 15 inch SS wheels with a 255 tire. Fit is nice, no wheel well rub. I think the later rears are wider though, might need more back spacing on the wheel or look into narrowing the rear. I'm looking to go with 17" N90's or a C5 Vette wheel of some kind, depending on what brakes I end up doing.

[LT1 OLDS]

I have an 87 Olds cutlass with the stock length rear. I have run 255/60/15"s on an 8" wheel, and 275/40/17"s on an 8" wheel (not recommended but it works) and I currently have 255/50/17"s on the 8" wheel. All of them fit without issue. You need to measure the rearends and figure out what offset wheel is going to work. The G-body rear is actually pretty narrow. Around 58" if I remember correctly. You may be able to run the 12 bolt with some late model Camaro or Corvette rims to save some money?

[LS6 Tommy]

Post deleted. I misread the OP...