There are two port sizes on small block heads, The 273 size, which is smaller than the 340 size ones. In fact the stock manifolds on my 87 Diplomat were very close to not sealing on the stock heads on my 65 273, top to bottom, maybe 1/8" overlap total. Both were untouched openings. I suspect those headers have the small port openings.

All you can do right now is make an adapter plate that'll seal to the head and the headers, short of buying new headers or heads. Which will kill the idea of gasket matching.

Unless the overlap at the top of the port is enough that you can oval the mounting holes and drop the header down to seal?

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.