Roll out length MUST be the same, or at least within 0.5%. I run drag radials in the back with a set of front 'skinnies' that I have double checked are the exact same circumference when on the truck and at the pressure I'm planning to run. If they aren't the same diameter then you will grenade the transfer case just like my friend did when he tried running the same staggered set from his 2wd which claimed to be the same diameters online but he never measured it when installed on the truck, turned out the fronts were 3/4" smaller circumference when loaded which doesn't sound like much.
For your tire sizes to travel 1 mile one tire will turn 628.64 times and the other will turn 626.7 times, your drive train will now need to make up 2 full revolutions of the one tire size, now travel 60 miles and it's 120 revolutions, see how it gets