Ya. Those are seat risers. Look to be aluminum. I'd sell them. I think those are the nicer or most expensive ones. IIRC.
I'm 6'3" and hear your pain. Even my stock seats without risers could be lower for my liking. If they were any higher I would have a real problem. Even now I have to crane my neck down to see a streetlight.
I went from 97-02 seats to 03-06 seats in my '99. (The early ones being the tear drop shape. The later ones being the more modern square seats you see in later Jeeps.) The later ones are supposed to be shorter. But my early ones were so old and worn out. That when I switched to the later seats it actually made me sit higher.
But anyway, as long as your '99 stock seats (if that is what you have) are in good shape - switching to the later seats may gain you some more clearance. As the late seats are supposed to be shorter than the early ones. And the later seats with there brackets are a direct bolt on to your early stage Jeep. So if you wanted to switch to 03-06 square seats you could easily. They also look better IMHO. Check
www.car-parts.com for seats. That's like the national clearinghouse for junkyards nationwide.