Evidently, grant makes a hub adapter for the 720:
http://www.summitracing.com/parts/GRT-5592/
I believe that will work with your nrg release. Don't they have both of the bolt patterns on them? For what its worth, the SRK 140 nrg hub(aka the 240sx hub) works on hardbodies, and as I recall they said its good for some earlier nissan trucks as well. Might be worth giving them a call if you cant confirm that grant hub will work.
Edit: Fail, grant hubs only mount the 5 hole grant wheels >.<
Unless you want to get a grant wheel, I guess call up NRG or pull your steering wheel and show us how it mounts.
Edit 2: Just found the parts list that came with my nrg short hub. It says supports all 510, 610, 810 and all nissan/datsun trucks 1986+
Hope it helps.