Lets get something straight, saying a relay is for a ford(or whatever) is no way to identify a relay.
The critical fact is, in a CUCV the GP relay must have no continuity between the body(it's mount) and any of the 4 terminals. The two small terminals must be either end of the relay coil.
There are a few other less important factors that play into this as well.
So, I have no idea what a gpr100 is, but I know that many members have purchased the GPR109 and st85 relay and it works (correct design).
edit, I looked at the napa site at a gpr100, and it has rubber mounts. This suggests to me that it may not be isolated. That would mean it is not correct for a cucv system.