You are just going to need to go to a junk yard and start measuring 5 lugs with same bolt pattern, have you measured your 720 to the d21 to compare? worse case scenario, if you find a little narrower one, then you can run an appropriate spacer without being too wide. I get what your trying to do, run same wheel pattern on both trucks, do not be discouraged, it's just not going to be as easy as just an axle swap, it might be but probably not. if you do find one that will work, might as well grab the driveshaft as well, might come in handy for the flange needed.