I just removed what I'm guessing was an original rear tire on my SC. It is an 11-38 (Tube is marked 11-38 too. No patches.) Good Year Sure Grip. It has the web lug pattern. Rims are in excellent condition. I think the tractor lived a fairly easy life.
How likely is this a nearly 60-year-old tire? It's pretty bald, and the eidewalls are very badly cracked/crumbling.