Weed,
I'll have to check my manual about the tubless part as I'm not certain about that. I've never heard of a 19.5" tubed tire... but there's lots I've never heard of.
I've got SEVERAL resources that state that 19.5's where an option on 1958 1 tons, and where the stock tires on the heavy capacity dually (Shop manual, restoration manual, my truck). The PO stated that the truck was all original, bought from the dealer (except the hydraulics for the dump bed which had been replace... and yes the dumpbed was a dealer addition Knapheide bed). The sticker inside my glove box lists 19.5" tires.
The rims have KH stamped on them (Kelsey Hayes?). They outer ring is riveted to the center disc (I know this is old style manufacture). The stud holes are the smaller 1/2" instead of the more modern 9/16" that you see today. The width is 6", not the larger size you see today (i.e. 7" +) to accomidate the wider lower profile 19.5" tires (i.e. 245 70R 19.5).
