Fan/Pulleys/Belts/Heads: It is all about what type of configuration you have on the front of the engine (along with the heads). The 36 engine would have had 1 wide belt and the crankshaft pulley would have located the belt right close to the timing cover. The 36 engine had water pumps in the heads - but they aligned in the same general vertical plane as the 37 - 48 pumps. This made it easy to put a later 59AB type engine in an earlier car - once one figures out the motor-mounts needed. So - if you're running a later 49-53 engine with the distributor to the side and the water pump belts further forward (as most the later pumps are . . . (so the belt clears the side-mount distributor), then you can have drama with an early car (pulley clearances, belts, fan, etc). In my mind, the 'best' setup is to put the early 'front of the motor' and sometimes 'center outlet heads' on the later motor (cam and all) - such that you can run a helmet or crab style distributor (off the timing cover), the standard 37-48 water pumps and the generator with the fan mounted on the front of it. This is by far the easiest way to setup these engines - and in the end, things just fit a bit better and in my mind, looks the best.
With that said - there are a ton of folks that have put a 49-53 engine (pumps, belts and all) in earlier cars - with all sorts of fun related to engine location, engine height, belt clearances, fan setup, etc..
I like to keep it 'early' and simple! Just makes things so much easier in my mind.
