ID the block

[Accelo]

"What I could find is the HC suffix code was for a 65-66 250hp 327 "

Did I read the suffix as HCR? That would make the block build after 1970, when GM went to a three-letter suffix, as they had used up all the two letters. Would know more if the block casting number wasn't hidden from view by the bracket for the PG kick-down.

The heads were manufactured with 2.02 and 1.94 valves. If you install 2.02 valves in this head, they will flow less than in the 1.94 valved head. The reason is GM cut back the chamber on the 2.02 heads on the intake side only. This unshrouded the valve so the larger valve to flow correctly. Very few conversions have the chamber machined. Typically, I just see it on the factory 2.02 heads. There is a tool to cut back the chamber wall, but most machinists do not bother.