The most common 16.5 rimmed 4x4 tire is the 37x12.5R16.5 Goodyear Humvee tire. For a while they were available used on the market very reasonable for the size.
After you get done cutting and patching all the rust consider a roll in bed/cab liner. I just finished my XJ Cherokee with a Monster liner kit. My 2 gallon kit did my hole inside extra thick. It turned out good as I like a less textured feel compared to Rhino or other really grippy liners.
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