The 56 engine will have the water pump mounted about 2 inches lower on the block than the 54 engine- - - -which creates fan and radiator clearance problems in the 1952 engine compartment. If it's been running that way, those problems were probably addressed some time ago. The water pump shaft had to be shortened or the radiator moved forward, to avoid radiator clearance problems, and a smaller diameter fan is usually fitted to clear the crankshaft pulley and lower radiator hose. The 56 engine should have a cylinder head casting number ending in "848" which is slightly higher compression than the 54 head would have been. Otherwise, the engines are very similar from 54 and 56.
Jerry
