narrowest 6 lug rear end

i got a truck im lookin for a rear end without having to do a irs i wanna do a straight axel the one i have now is a 82 datsun 720 it measures 54 inches drum to drum on the outsides. is there anything more narrow than this maybe the courier? is there any 6 lug irs from a new amigos or navigators that could be shortened?