When it comes to front ends, and rearends, why not make the body with these off. Then make seperate front, and rear, parts for the different cars. I would imagine it would even make it easyier too cast.
Then You also have the different front/rear, for other versions of the '73/'74 Chevelles. Maybe even El Caminos. I can't say I don't like the Coupe, but those SW's, sedans, and trucks ain't bad either.