A photo of the underside of the front steel plate between the timing cover and the engine block would be helpful. Some of those plates are already drilled for attaching the flat rubber mount that sits on the front crossmember. If not, you can use the front plate from your 216 as a template to locate the bolt holes properly. Swapping the 216 block plate to the 235 is also possible, but that involves removing the timing cover and the camshaft. The square holes in the plate for carriage bolt type heads aren't really necessary. That large diameter harmonic balancer weight might cause some difficulties with fan clearance when the water pump adapter is installed, but the 216 balancer can be installed on the 235 engine. The press fit is the same, or you can drill and tap the crankshaft snout for a balancer installer and/or a center bolt. Using the 216 balancer will also allow you to run the original wide fan belt, generator, water pump pulley. etc.
Jerry
