David, it is rather easy to explain. The roof is a vacuum-formed roof that I made using a "buck" I formed out of sign foam. I used a version of this roof on the '62 Buick Electra 225 And on the 1965 Pontiac Grand Prix And on the 1965 Riviera that isn't quite finished yetNow on the 1962 Pontiac CatalinaAnd now on my 1962 Chevy Impala.On the Electra 225, I was able to lay back the "A" pillar to accommodate the new lower roof..... same on the Grand Prix and the Riv because on these two cars the "A" pillars were straight upright , But on the Catalina and the Impala, the "A" pillars are curved and did not suit the new roof design, so I had to fabricate he pillars out of 3 pieces of plastic stock one flat, one larger half round and one smaller half round for the trim with a metal rod on the inside to get it the support necessary. Does that explain it better? I varied the side window shape and the rear window treatment to make it look like slightly different roofs.