I shot an email off to Jerry Lemond (a known Isuzu Guru), asking about half shaft interchangability, part #, etc...
Here's his reply...(edited, for length)
THE HALF SHAFTS USED ON THE VX, ARE VIRTUALLY IDENTICAL TO THE SHORT WHEEL BASE TROOPERS, THE FR DRIVE AXLES HAVE DIFF PART NO,S THAN THE TROOPERS BUT THAT IS MOST LIKELY BECUASE OF ONE OF TWO THINKS , EITHER THE MANUFACTURER OR WHERE IT WAS MADE , A LOT OF THE PARTS LIKE THAT ARE MADE IN BOTH JAPAN AND IN TAIWAN, AND THEY WILL BE INTERCGANGABLY BUT HAVE DIFF PT NO,S ON THEM, I AM ALLMOST CERTAIN THE SAME YEAR TROOPER AXLE ARE THE SAME , BECAUSE THE FRT AXLE HOUSING HAS THE SAME PT NO FROM 95 THRU 2002 ON THE TROOPER AND THE VX, SAME WITH THE REAR AXLE, THE VX HAS THE SAME PT NO,S AS THE 95 THRU 97 TROOPER ,, THE 98 TROOPER WHICH IS MISFIT ALL IT,S OWN, AS IT WAS CHANGED BACK TO A JAPAN BUILT UNIT IN LATE 99