Duane, first off, Welcome to the site and glad to have you on board with us!
As for your question, the GT-2 series wheel combination was 4.80/4.00-8 traction type front tires and 6-12 traction rear tires. Basically the front tires had a diamond shaped tread pattern on them and the rears were the bar or ag type tires.
The GT-3 series wheel combination was 16x6.50-8 high flotation type front tires and 23x8.50-12 high flotation type rear tires. If you are wanting to match the original tire code of GT-2 for your tractor, you will need the narrow 3-3/4" front rims and the narrow 6-12 rear rims for your tractor. The GT-2 traction tires for both the front and rear can be found on eBay as well as Miller Tire Company who specializes in custom or hard to find tires.
Good Luck with your hunt and please post some pictures when you have the chance, as we all would like to see your machine!!
