The stupid is everywhere, I have experienced the same difficulties when attempting to have old tires mounted, if only to just hold vehicles up off the ground; the result is that I have realized I must mount them myself. I even have purchased a tire mounding-dismounting machine, particularly for my truck tires, as they really are a little much to do by hand.
Also many establishments will not mount a tire size not listed (in their computer
) for a particular chassis by the O.E.; nor will some sell and mount tires on wheels unless the vehicle is present, this in order to establish proper application of the product. So I guess with these policies in place, you'll get a big no!, if you ask them to mount your Polyglass N50's on your 10" rims for '70 Camaro?
And good luck, at getting anyone these days to get near the 'split-ring' rims (sometimes, but improperly referred to as "split-rims", though there is such, and I have some vehicles with such, but that's different, but they won't touch them either!) on the older trucks.
Thanks, to the greedy self important P.I. Attorneys and the greedy low-rent clients that they attract, they have corrupted this portion of the judicial system into a money-making revolving door industry that just nullifies the righteous instances that deserve attention, and as presented by the O.P., but not limited to, interferes with the common function of our society.
Scott.