I think your '55 will have pulleys for a 1/2" belt and if you want to retain that, you will probably have to have a custom pulley made.
If it has newer 3/8" pulleys, there are lots of options, nothing that is a direct bolt in replacement but the bolt pattern and pilot diameter is very common. You would have to find one that can be shimmed to align with the other pulleys or as above, have one made. You probably want something 6" diameter or smaller. The stock pulley is something like 7 1/4, if I remember right.
To get an idea if a smaller pulley will help, you can observe coolant flow in the radiator when up to temp. You need to be careful that you don't burn yourself while doing this. Use common sense. If it doesn't look like much is going on, try elevating idle speed slightly. Alternatively, you can try elevating idle speed when it is getting hot, to see if temps start to fall or stabilize. If an elevated idle speed helps the situation, what is happening is the pump and fan are turning faster. A smaller pulley does the same thing but allows it to keep the correct idle speed. This is also under the assumption that there are no other problems with the cooling system.
Lawrenceville, GA