rear end help

[texastrendz]

okay guys i got it apart, i want to get the housing powdercoated this week and get it reassembled. what i have is a stock 12 bolt out of a 72 truck. what i am installing is a 5.3 motor with the transmission. i dont know what tranny i will get yet. i will be running a 275 55 17 rear tire. i was hoping someone can help me with what gear to put it in, and if i should install a posi unit while i got it apart. i want to run the trans that will come with the motor that way i will be plug and play with the wiring. this is all new to me as you can tell, any help would be great thanks again, Daniel.