I was wondering if the doors on a 70 cutlass supreme (notchback) interchange with the holiday (fastback) model, this is a 2 door car. Thanks

 

Yes, all 70-72 hardtop, Supreme, and convertible door are the same. If you are worried about perfect points at a high end show, the first 2 or 3 months of the 70 model year had a slight difference but this is trivial and something only a high end judge would even know about. Nothing to worry about if you are not building a 1000 point car or if yours was built in November 69 or after.