Hey Bill,
The difference is semi-floating rotors or solid mount rotors.
My fronts are solid mount. I did a lot or research on the difference and everything I read said unless you're racing on a track there is no need for them. BUT my front ones are NOT pre '93 size. Their 298mm or what ever the late model ones are even though they look smaller they aren't. They work great, look great weigh less and cost less too... I am HAPPY as hell with them. WhiteBuffaloracing.com just have good pricing. I have priced a lot of stuff there including my Barnett kit and it was A LOT cheaper from them. Plus Mikes a good guy and will work for ya!
Good luck,
Chris