Well, those heads generally have inferior valves to those on a turbo 2.3 head , so the valves don't hold up so well...or hardened valve seats. Plus, I could be wrong but I think the valves are smaller too.
Valve sizes are the same between the 2.3Turbo and N/A. Chamber volume is indeed less for the N/A which will raise compression, but like RedLX, I'm not sure how high it will go. If all you have is an N/A head, take some material off the "point" of the heart to increase the chamber volume, have the machine shop do a valve job including putting the turbo spec exhaust valves in, and have fun. If you have the old turbo spec head, just cc a chamber and make sure the reworked chamber on the N/A head matches, and you should be good to go. But again, unless you like burning exhaust valves, find a set of the Inconel valves if you don't already have a set.