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I’ll probably need three wheels, one for the non-existent spare and two to replace the split rims (hard to find anyone to work on them).
There is a consensus among many that the best method for fitting new tires and wheels (especially on the earlier single-axle trailers) is to take the trailer to a tire dealer who also sells wheels. Allow a representative of the dealer to take the measurements and act as your representative in the purchase - - the idea being that if the wheel/tire combination doesn't fit when it arrives it was the dealer's employee who made a mistake in measurment and not you - - thus there shouldn't be any question about returning the non-fitting merchandise. I have followed this method with my '75 Eldorado tow vehicle as well as both trailers - - it saved me from having to buy a set of wheels on the Cadillac that were ordered with an off-set that was not quite right. The clearance can be particularly tight on one side or the other of many earlier single axle trailers making the fitting of modern tire and wheels even more challenging. You will want to be certain that the dealer's representative is specifying trailer wheels with a 2,600 pound or greater rating along with ST rated trailer tires of appropriate weight carrying ability for your coach - - the '52-'53 Flying Cloud had an empty weight of 2,540 pounds - - likely fully loaded weight will be somewhat below 4,000 pounds with careful packing. You can find information about hitch and empty weight at: Airstream Weights and Measures
Good luck with your tire and wheel project!