Inky,
Availability is limited; I got a quote from my local Allen Tire distributor about two years ago:
8.25 x 20 bias were about $120 for highway tread (fronts) and about $150 each for lug (mudgrips)tread for the rear.
I think I saw 7.50 x 20 on the Delta Tire site, but have not contacted a local dealer for pricing.
Also don't know if the 8.25 tire is too wide for the original 5" rims... ???
You can get "correct" 6.00, 6.50, and 7.00 x 20 tires from "antique tire" merchanst like Universal or Coker, but I think the 6.00 x 20 is running about $150 plus shipping.
Tubes run about $20 each...
None of the local tire dealers are stocking 20" bias any more, even though older trucks running them are still a common sight on our roads...
Good luck!
