If it's dual rear wheel and/or 8-lug (probably 16.5") wheels, tires should be Load Range "D" or higher. D is about as high as you'll commonly find in 16.5" and E is very common in 16".
I saw a Dodge with 16" wheels on a visit to a lighthouse and I ***SO*** wish I'd hunted the owner to see what they came off of. If you have a C THAT old and it's a keeper AND you need tires, it'd be good to find seven (assuming dual wheels) 16" wheels. You might even be able to find them with serviceable tires.
A Dodge dealer should be able to de-code the information you need for parts. We had a 1971 One-Ton Dodge Window Van and its model was simply called "B30". A good counter person at NAPA could possibly help too. My guess is if you go after "One Ton Dodge Van" (Cube Van if you're lucky) you should be able to get virtually any part you need.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB