The manifold I have is for 70-71 B or E-Body. Don't remember which car I got it from, but I bet an E-Body.
I took the 8 3/4 from the same car and put it in my 67 fastback in the late 70's.
I did the big block swap when I was 16, with the help from guy's that actually were around during the early Mopar glory.
My uncle raced a 63 Fury Max.