Rich, I think it's right at 75", counting the sidewall bulges. The tread width is still just under 72", so a 6' box scraper will just cover the tracks if it's centered and I'm going straight. I'll try to remember to measure it tomorrow. I've got another lot to rough grade. I'm not looking forward to the 90+ they say the temp is going to be, though.
I've not had the slightest trouble with anything other than the backhoe. If you've got over 2" of clearance behind the tires with the implement, it'll be fine with the new tires. FWIW, the Freedom Hitch adds 4" or 5" of clearance, so I you use them, any clearance problems that you might have had on 3-point mounting implements go away.
Yes, the 19.5LR24's and 11LR16's are perfect matches, at least on the L-series HST's. You need to find out what the mechanical ratio between the front and rear axles is on the tractor you're looking at to be sure. Call Kubota to find out and let me know - then I can tell you for sure.
Mark