Grigg, I added tandem setup pics to the photbucket. The rear axle is dead. I could not find an ID plate. But who know under all that grease and grime there might be one. I wish I could help more but this is all new to me.
You are correct about the wheels. Rear tires are 9.00 x 20 and the front tires are 8.25 x 20. Your article "New wheel for Advance Design "Big Bolts" mentioned 1956-1959 1.5 ton trucks to find one piece rims to fit 9R22.5 radials. Any other chevy model for those years i.e. school buses? Are the Budd wheels stud-piloted or hub-piloted?