361, 383, and 400 all have the same stroke. I'm not sure if the main bearing diameter is the same (I think it is) then you can interchange the cranks. I would also try to get the vibration damper from the crank that you buy also, just so you have the proper one to go with the crank.
As far as different between 2 bbl and 4 bbl, if they are both cast then I would bet that they are the same and completely interchangeable. I still recommend trying to get the vibration damper and crank pulley with the crank if they have the original ones for it. It's always better to have two sets of parts to get things together, than just one...