rear end help!!!!

[x73mach1x]

i have a 73 mach 1 with a open rear end and i was think about buying a locker for it???? which lockers are good for a street/ strip car and how much would i be talking to buy one??? i dont know what kind of rear end i have in it how do i identify it???? one last thing would i be better off just buying a posi out of a junk yard??? thanx