Emma,
Heed what DrewP posted.
Ask your engine builder if he/she ever had an over-heating problem using an adapter plate with an older style water pump (on a block that had been carefully cleaned out). I bet the builder never used one and is stating hearsay or is just stating an opinion.
The exhaust manifold used on all 216s and on earlier 235s had a straight-down outlet (later 235s and all 261s outlet angled towards the rear). There were also differences in exhaust/intake port diameters.
