If it will take the 4.56 third member from another Isuzu, it will take the locker (RD44) too. I have moved my 4.77s from an 89 Trooper to an 88 Trooper to a 94 Trooper - all the 26 spline axle. Those 3rd members will accept the RD44. Now, the VX cast iron housing may have some interference problems with the locker, but that wouldn't prevent you from swapping to 4.56 gears and an earlier 3rd member at the same time (2 birds, one stone).
-Tad