This stuff is not all that precise of course, even though tenths of inches are quoted. I notice that your 6060 Grand has one choice of 54.5 and that plus the 17.1 inch tires makes 71.6 inches outer edge to outer edge. The 74" blower running behind that will clear theoretically 2.4 inches more than your tire path width. Two inches "ain't much" when there is snow all over the place and you may well want more clearance by going to the 51.2 spacing on the 6060 which adds 3.3 inches, a little over an 1.6" on each side or leaving the tire path a total of 5.7 narrower than the nominal width of the blower. It becomes a personal preference thing at that point as to what you want and whether you really care about small differences. I recommend you have the dealer deliver the tractor with the tires set to whatever width you decide on, agree on liquid in them or not, cast metal wheel centers for weight, if you chose that option, etc. He really should set this up the way you want it. Moving rear tires around yourself is not that much fun. Of course I do not know your operation, how much help you have, etc. I would be very surprised if the dealer in your area lacks quite a bit of experience with snow blower applications and he should be able to provide the direct experience/advice. I have no idea whether you have any steep slopes or significantly uneven ground on which this machine will be used. I am always more comfortable the wider the rear tires are apart. By the way, I like the inner edges of my front tires and inner edges of my rear ones to match in spacing.