I'm thinking that the part should be the same on any 3.5L or 3.2L engine that Isuzu used. You could take yours in to a local boneyard & compare it to one they have on the shelf.

The other alternative is to install an inline aftermarket thermostat like deermagnet did ... & then cap off where the thermostat housing fit (with a fitting installed of course to attach the hose to).