The 78-80 radiator core support does roughly interchange with the 81-87 body - they use the optional aluminum ones with drilling a couple holes to lighten drag cars. (The support rods for the header panel)
If you wanted single headlight, look into the 78-79 regal... 1980 was the only year of the old style with a quad headlight.
The hood and header panel can swap onto your existing core support, BUT, you would need to do some custom work to the fenders... I've seen it done in the past, guy spent a ton of time grafting the front 81-7 onto a rear 78-80 but looked slick when done.
Bumpers can be made to fit, if you look at the shocks and bumper core they're slotted at the bolt holes on both ends for adjustability.