I'm curious as to what parts from a 72 cutlass supreme would fit on a 70 cutlass S? I know nothing from the rear, but what about the front fenders, radiator, front wheel wells, or front vore support?

 

The rear bumper and tail lights will bolt up, although the 1970 used 2 vertical lights and the 1971-72 2 horizontal ones . Then back to the front, the fenders will bolt up fine although the 1970 didn't have crumple ridges and 1971-2 do. That's the little bumps under the hood, along the side lip that the hood covers. The front bumpers will swap although the blinkers are different. To swap over anything else on the nose you'll have to change the radiator core supports. Hood, grills, headlight assemblies, etc are all different from 1970 to 71-72. But... if your willing to change that core support the nose from a 70 will bolt up to a 71-72 and back the other way too. John

 

Just to expand a little on the last post, the two cars are mechanically identical. Frame, suspension, brakes, etc. all interchange. Body-wise, the main difference is the roofline, rear quarters, and trunk lid. Allowing for the annual differences in grille, core support, hood, and bumper as noted above, the Supreme is identical to a Cutlass from the doors forward.

Even headers interchange.