Re: 1956 Advice...
If ya found a bus that is good for you..... buy it. Find other folks who have the same bus and ideas. there are several yahoo GMC bus and engine groups.
Ask all about parts and people near your travels. Become very connected to the bus. Learn all ya can about everything. Make a connection with an old GMC mechanic. It is not necessary to know everything about the bus, just where to get parts and information. Have a great trip with support. I think old crown buses use the same engines. Best wishes. Frank