I recall it being an iron case vs a aluminum case for the front axle. The iron case wasn't exclusive to the ZR2 but it was on every ZR2.
There are honestly too many potential weak points on a compact pickup to push the limits.
The track width is wider but I believe it is still narrower than a 1/2 ton 10 bolt so there is non guarantee that the axle tubes are as strong, or the axle shafts, or the beatings. Most of that is easy to check.
It is the stuff you cannot check, or is difficult to check, that will be likely be the limiting factor. Spring-under suspension ratings, frame ratings, brakes, etc.