There is some info here:
http://www.contour.org/FAQ/FAQ.php?s=models
Perhaps the easiest way to tell (if you have your stock wheels) is to look at the wheels.
The 1998.5 + had good looking Cobra style 5 spoke wheels and the 1998 had poopy looking wheels (
).
Edit to add: I assumed you meant SVT. The distinction is usually made with regard to SVTs.
