a poly does not fit in an A-body. Why do you think the design of the heads was changed? One reason was to fit it in the A-body in 1964. (273)
Poly is just too wide. correct, the back of the 63 and latr is exactly the same as any 318
A good place to find a 727 is behind 66 poly (65? maybe too). Motor mounts the same 63 up poly. (not sure about earlier ones)
