There are two or three problems with using a 235 crankshaft in a 216 block, none of which are beyond solving, but it's going to require some serious machining. It's definitely not a drop-in fit.
1. The thrust bearing in a 216 is a bit wider than a 235. It would be necessary to machine the flanges of the #3 main bearing on the crankshaft to accommodate the 216 bearing. The diameters of the mains are the same, so simply machining the crank would allow the shaft to fit into the block and turn properly.
2. The 216 block is about 1/8" shorter from the center of the main bearing bores to the top of the block than the 235. Since the connecting rods in a 216 and a 235 are the same length, that would make regular 216 cast iron pistons stick out the top of the block or hit the cylinder head and lock up the engine.
3. The 216 oil pump is a very low volume item. It would be wise to install a higher-volume pump, but the Melling M-45 pump that would be a bolt-in swap won't clear the oil pan. That's why later model 235's with the big pump have an offset in one side of the pan rail.
All the above problems can be solved. I'm currently building up a "216" with a bunch of radical internal modifications which can't be seen from the outside, but if I were having to pay a machinist for his time, my checkbook would need a life support system! It will end up as a 235 cubic inch engine in an original-looking 216 block, with 235 aluminum pistons and a 235 crankshaft, plus an improved rear main bearing seal and a few other sneaky tricks. I'm using shorter connecting rods from a 292 engine to solve the block height problem.
Jerry
