Post mount rigs can be a pain sometimes.
If that can't be secured well enough and you have to replace it I think you need the post from a JTruck, might even be year specific but I'm not sure on that part. They are slightly different from the Wag/Chero posts, that I do know. It might not be enough to matter.
It's a tough call on replacing it:
If it was me and I just had to do one, I'd try to find a match. If I had to do two (or more) I'd probably replace the entire rear post setup with box type hangers from a newer JTruck, modify something from another truck, or just build something from scratch.
2000 Infinity QX4, 3.3L, MPFI, 4 speed auto, 2 speed Nissan tcase, Unibody, IFS front, 4 link rear solid axle with 255-70/16s
IFSJA WMS PROJECT
EARLY WAG LIFT SEARCH
Self Inflicted Flesh Wound
...Pay no attention to these heathen barbarians with their cutting torches and 8" lift kits!...