Will a 64-65 Cutlass rear-end fit in a 68? Length? Spring mounts? Control arm mounts?

 

It will bolt in but you will need to use the coil springs from the 64-65 rear end as they bolt to the housing. 67 and newer just slip in place,.

Henry

 

You can use the 68 springs,and bolt them in place,like they did in 65. The 65 springs are open at the top,and will not fit the 68 frame correctly.
The 64-65 rear is 5/8" narrower on each side,compared to the 68 rear.