Spring perches changed on the rear end for 67.
64-67 Cutlass, LeMans, Skylark, Chevelle.
These are all direct bolt ins except that you will have to use 67 springs on a 67 rear.
68-72 are an inch wider-----for these rears you will also have to use the 68+ springs.
Any of these rears will bolt in, but for the later ones you will have to keep a close eye on the wheel backspacing if you are running oversize tires.