Thanks Sam, Steve and Todd.
Todd,
I got the tires off Ebay.
Here is the sellers page. Interestingly enough, no items for sale right now. Shipping was free, and I paid $64 for the pair with tubes. Best price I found.
The tires themselves are Deestone 4.00-8 tires. I see they offer them in both 3.50-8 and 4.00-8.... I wanted the wider tire so I went with the 4.00, but honestly I don't know whether there is any difference or not. Price was different. The 3.50's are quite a bit cheaper.... but I've seen other tractors with the tri-ribs and I thought they looked funny and extra narrow. Maybe different tire brand, or maybe they were the smaller tire.... either way, the 4.00's were quite a bit taller than the ones that were on it, so it raised it back up to a more regular height. They were at least 2" taller overall, but when plowing in a dead furrow, any height addition is good. Yet another reason to go to 8.50's on the rear. Taller.
The disk project will be fun.... if I get to it. I wasn't going to bring it up, but Zippy wanted to know what the plan was with duals. I'm just not happy with the Brinly tandem disk, and I don't want to hunt for a 3pt Brinly. Besides, from what I see they have the same issue. Not large enough blades, wrong blade dish, wrong gang angle. Jerry Collier is the only one I've seen who rebladed his disk with the 12" blades that I want to use. Really improved it.... but it's still just barely as wide as the tractor, and looks like the gang angle could still be improved. Besides.... if you don't count the time I'll have in making it, I'm certain that the steel won't cost any more than the price of a Brinly cat 0 disk and new blades for it. Here's to hoping I get to it!