JEFF - I know you've posted pic's of all your 169, the GY Super Terra tires have the 45 degree close spaced lugs right? They're a good tire, as good as any GY has made, but IMO still jot as good as a Firestone.
I think it was Ditch Witch that used a lot of those GY's on their trenchers. If they're 4-ply tires you have, you're in good shape. I've always felt GY tires had weaker casings than other brands, so more plys are better. My 23-8.50 'Stones are 2 ply, the 26-12.00's are 4 ply, and O only run 6-7 PSI of air in the 8.50's and 4-5 in the 26-12.00's. You could almost run the 4-ply without air but the casings would flex so much they're war ot sooner... a little flecing is O-K, more than that is not.