Rear end question.

[83oldsguy]

I am wondering how to tell if a rear end out of an 85 monte carlo ss is an 8.5 inch or a 7.5 inch and if it is an 8.5 inch will it bolt right into my 83 cutlass that has a 7.5 inch? i know it will bolt in but will i need a sorter driveshaft?

 

[pontiacgp]

Monte SS never came with an 8.5 but they did come with a 7.625 rear end which fits in the 7.5 housing...and yes you'd need a driveshaft 1" shorter for the 8.5 rear end