Can you use 56 heads on a 55 engine? If you use 56 intake?

 

Not a expert for those years. But mt brother has a 56, and I know years ago, he bought a 55 parts car, and we switched so parts, not sure, as it was years ago, but the 55 motor was a 2 barrel, and he put the 56 4 barrel on it. I thought that all those 324 motors were the same?

 

As far as I know, the big difference between the 1955 and 1956 324 heads is the size of the valves. The 1955 heads have 1.750" diameter intake valves and 1.433" diameter exhaust valves. The 1956 heads have the same intake valves but have 1.562" diameter exhaust valves.
There is also a change to the intake manifold. If you put a 1956 intake manifold on a 1955 324, you need to use the 1956 valley cover which has a deeper indentation to accept the 1956 manifold.