Whatever you do, I wouldn't recommend replacing just one head unless you know what the other side measures on thickness - or unless you want to spend an absolute minimum. You can measure it on the engine at the outer flats near the exhaust ports, but it ain't easy to do and is much better done off the engine and clean. If you have to replace one head, it's better to pull a good uncut pair - then while you're at it, you have a good excuse to rework the entire top end - that is, if you're so inclined.

What does the cam journal look like where it seized? You may need to replace the cam.

It's interesting that the head was on a 1990 Montero. I don't know that I've seen an original head from a 1990, but that was the year they discontinued the EGR system. It may be coincidental that the EGR and MCA jet head systems serve a similar purpose, so I wonder if some of the '90 models had jet valves as standard equipment..... never heard that they did, but I can look for an interchange on the heads tomorrow. I would think if that was standard in 1990, I would have run across a reference to it by now, so I doubt it was a Montero OE head.

I guess it could also be an early Chrysler 3.0L head. Do the rockers have roller tips, or a flat slipper as a cam follower?

Frank