They can be installed. The Gen III seats themselves are higher and will move you forward slightly. Like Shelby3 says, you'll have to cut the mounting tabs off the new seats and fabricate brackets for them. Absolutely great mod IMO. Here are some pics of my 97 GTS with Gen III seats.
If you have absolutely no room to go higher then it probably won't work for you. You may be able to lower it another inch if you eliminate the slider rails but it'll be difficult if not impossible to access the rear bolts. Where there's a will, there's a way. I'm sure someone out there can do it.