Specifically talking about 1970's and newer cast iron, GM stock SBC cylinder heads. Not knowing what to call it other than the intake manifold mounting surface of the cylinder head...are they all cut at the same angle...no matter what year?
Unless the head has been extensively modified and milled improperly. Then maybe the intake to manifold angle would have to be milled to match... The only other variable would be the bolt angle for the intake manifold bolts changed in 1987 I believe then later in the 1990's to the Vortec style.
Some heads get modified to improve performance. I just sold a set of 462's that were modified to 18 degree heads. Once heads have been modified to 18 degrees no "stock" part will fit. Everything from the headers, to the intake, to the push rods either have to be extensively modified to match or custom purchased.