[JamesMA]

FWIW, I followed up with my Parts guy and while there appeared to be plenty of front wheel spares (30+), he told me that the computer showed that the number of 403M rear wheels available as spares was less than 10, to which added an unsolicited "That is not good." He still thought he could get them but that it would take 2 weeks to get them at the earliest (if the they were still actually available - you know how that is), but I decided to go with just go with the 20". Hope it all works out for people.