So once again I'm a little biased on an AutoPuzzle.
The custom here is based on a 2nd-generation Pontiac Firebird or Trans-Am.
I would know. I owned one.
The interesting thing is that the taillights and rear bumper came from a 1979-1981 Trans-Am, but the rear window doesn't have the wrap-around shape - thus indicating the car used for this monstrosity was built before 1975.
The car is called "Celestial" by Ian Etheridge, and was built on a 1973 Trans-Am.