i have a 70 gran coupe was a 318 car and has what i think is a 8 1/4 rear(deff not a 8 3/4) i have been building a 8 3/4 out of a 69 road runner to put a lil bigger tire under the gran coupe what i need to know is ...will the shock plates maybe even the u bolts from the 8 1/4 fit the 8 3/4 or will i have to track some down(the road runner rear didnt have them) and if i do have to track them down what other cars (a,b,c body) would also work?
thanks guys

8 1/4 plates wont work. I think the u bolts arent going to be wide enough either. I just did the change on an a-body and had to find new plates and u-bolts. I think the plates will work from most 8 3/4'S. I used one from an early 70's c-body but I cant remember if I used it on my e-body or the a-body.

Yeah they fit, the only time you have to change is when you have a 7.25. If you are unsure of what rear you have the 7.25 has 2.5" tubes, the 8.25 & 8.75 both have 3" tubes.

how do you tell a 8.25 from a 7.25?

My scamp must have had a 7 1/4 in it. Sorry for the wrong info.