8 3/4 rear end gears

he i recently found a 8 3/4 rear end im going to pick up this week.(its a really great story).but anyway how do i tell what gears are in it?Its drum to drum and off an A body.Im putting it my 72 dart.will i have to modify anything(drive shaft)?I want the car to be able to smoke the tires,is this possible if it has stock gears?what gears are stock? :tongue10:
any help would be great....Thanks