Level of difficulty changing 8 3/4 gearing

KIII said
1973 Dart Sport, 340,727, 8 3/4(2070741). My issue is that its geared way to low. The previous owner said he was'nt sure whats in the rear,maybe 3.73? Question#1. How hard is it to change out the rear gears? 1 being an oil change and 10 being an engine swap. #2. How much? #3. Where to purchase? Thanx.

Are you running a sure grip? If not it would be easier to just buy a good used assembly and install it. That would require no setting up the gears and if you shop around would likely be cheaper than buying a ring gear and pinion. that is the big advantage of having a 8 3/4 rear end.