you definately need a v8 rad. also. if you don't have info on the rebuild, check to see if there is a rebuild tag or work order number stamped somewhere on the block. ask around who might have that kind of stamp. you may be able to get some info from the builder. when you take the manifold off to replace the gaskets, check to see if the intake fits the heads. sometimes the head gasket surfaces get machined and that makes the mating angles to the intake manifold wrong. it can leak oil or air. both could cause the problem you are having. a lean running engine will run hot, also oil sucked into the manifold plenums will cause smoke. it happened to a friend of mine who had an olds engine. the shop had to plane the heads a bunch and put them on anyway. mostly because they couldn't find another set to fit. it ran hot and smoked, aspecially when hot because the oil got thinner maybe.
just a thought.