will this squarebore bolt to spreadbore intake?

Short answer is no. Yes it will bolt on, because of the dual bolt patter, but the primaries (at least) won't open. I once ported a 71` 340 manifold to work with an AFB. It has "pear" shaped openings, I just ground the inner corners of the primaries to clear the butterflies.

You should be able to easily tell, just by putting the gasket for that carb on the manifold in question