I know it's NOT a first gen F-body 67-69(camaro/nova/firebird) and it's NOT a G-body 1964-1972 (chevelle/cutlass/GTO/monte carlo/etc).
I'm betting it's off a 1970-1981 Camaro or an X-body (nova/omega/etc).
1st gen Camaros and all Novas are rear steer. 1st gen A bodies (Chevelles didn't go G until 78). It's probably a second gen Camaro/Firebird. The spindles look pretty tall and the steering arms look to be cast as one piece.
The brake pads should be D52s. Most all upper control arms use the same bushings. Your lower rear bushings are round which points more to the 2nd gen Camaro also.
Second Gen subframes are as popular on street rods as Volare front ends are on fat fender Ford trucks.