The difference in diameter is 6" between the stock tires and 4.80-12 that I looked at, the stock are 26.3", the 12" are 20.5". Its fitting over the drums that I question. I considered a set of empty rims too, and may go that route if I have to, the only downside, the area in the barn where it will actually rest is dirt, the rest of the barn has a concrete slab, so getting it back out may be a challenge, if the rims dig in, they may not be able to get up over the edge of the floor. A few sheets of 3/4" ply may solve that issue as well.
They might fit if I flip them over, provided they clear the fender. I have a few months still to figure this out, but would be nice to know, would hate to buy a rim/tire, only to find it doesnt fit and be stuck with it.