Steve there is a cap across the top of the radiator support that makes it impossible to put a radiator in there without cutting it out. Most of them I have seen are spot welded.
Its easy to put an old style valve cover on the new engine. Its not perfect, but with the old style water pump with adapter which you can even get in a wider belt groove, you can come pretty close.
I've even seen some where they cut out the rad support cross braces. Thankfully that is just 3/8 round stock and can be made with little effort. That radiator support is made the way it is for several different stresses put on it from several different directions. That cap is important for side to side, the cross braces for twisting, etc.
What's done is pretty much done by now. Not alot of people anymore seeking out swapping from 216 to 235. When I find them I encourage them to do it right, and I fix every one I get my hands on. It was done out of necessity back in the day I suppose.
