Machining the 216 cap separately from the block to match the 235 would be pretty easy, as well. You don't have to work around the block. Also, installing the narrower cap to do the machining would let you cut the block web till the cutter just "kisses" the narrow cap. Using the 216 cap should also mean you wouldn't have to line bore it to match the block, as that would already be taken care of if it was the one that was originally on the engine.
