Tire sizing

I have a 93 f250 that I'm putting 350 dually axles under and a flatbed on it to build a service truck. I plan on running 20" eagle alloy dually rims. The truck will probably be lifted slightly, but not too much being that it's a work truck and I will also be getting a snow plow for it. My question is what size tire you guys think i can get away with? I don't know the OBSs like I do the superdutys. Below are some pics of the truck, the dually bed, and tires I'm lookin at


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i can clear 36/12.5s on mine with no rear block just springs and an ad a leaf up front it sit level minor rubbing