You will need the complete rear end if yours is a 7 1/4, upper control arms, spindles, calipers, backing plates, rotors, master cylinder and a disc brake proportioning valve to start with.
If you change to some rear end different than your car has in it then you will need a drive shaft also. I wouldn't waste my time putting in another 7 1/4 if that is what you have.
If you have the 8 3/4 then you will need backing plates, all brake parts, drums and new axles made.