yep its the 9.5 (or 9.75 can remember which size it is). the 2wd is going to be slightly skinnier than a 4x4 axle but you could just run wheel spacers if need be. is it the 6 lug or 8 lug? take a picture of the differential housing, if its kinda oval shaped its the 9.5, if its irregularly shaped its the 10.5 (81 had the full floater, but the semi-floater might not have been around at that time).