Once you have the rust formed in the tank its very difficult to get it clean. I have had them derusted in a tank of caustic chemicals, then used the tank liner products available. It looked good when I was done and worked fine. I talked to the guy who purchased the '34 and 20 years later he had a rusty mess and ended up replacing the tank. So if you decide to clean yours I'd suggest giving it a visual inspection every couple years.
