What do they do with inner fenderwells when swapping B.B into early, skinny A-body?

Actually, Bob, there are factory exhaust manifolds that you can use in even this tight installation. I forget the part number and application at the moment. Of course they wouldn't flow as well as some good headers.

But if the inner fenders go, as you say, what supports the outer fender, the radiator support, etc.? Sorry if I'm being dumb.