" . . . difference in the exhaust manifold off a 235 or a 216 . . . "

Different intake ports and carb mountings on some of the earlier 235s. I think the exhaust ports on 216s and earlier 235s are the same.

The angle of the exhaust manifold's downward tube is different between newer 235s and older 235s/216s. The intake manifold has at least one difference in bosses for later 235s/261s.

Casting/serial numbers is the best way to proceed.