That bicycle isn't a 1998 model R500, its older, probably in the 91-96 (?) range, just guessing. It has the cantilever chain stays, look at the Vintage Cannondale site and check the model year by the serial number, if you can get it: http://www.vintagecannondale.com/info.html I own a '97 R500 and the frame isn't as pictured and the 97 and 98 are pretty much the same bicycle, just a heads up before you buy.

As to it fitting you, saying you and your buddy are the same height won't give you an accurate picture of its fitting you. His inseam and yours may be different as well as your arm or overall torso length. Stand over height doesn't decide whether it fits you, as Rollcall NY said above. $400 isn't a bad price for a good condition CDale of the probable age, and these aluminum forks are pretty well engineered, just a harsher ride than a carbon fork and steerer. A replacement carbon fork with modern stem and headset isn't that big a problem, either. My 91 SR300 actually was a good riding bicycle, I'd pick up another if I could find one.

Bill