6.5" with 35s can be a good combo. With 4.5" backspacing you will rub when at full turn on the lower link. 24 hrs is way too ling. They should be able to do it in 12 hrs if they are set up for it. If they have a hoist, then 8 hrs. 1000 per axle is average for a gear change with lockers in the deal. Otherwise, too steep. I would add, that since you
are in the rust belt, that is with no broken bolts due to rust.