Matto said:
...Power difference between 98 and 99 is 215 HP compared to 260.
Well not quite
98 Mustang GT
- 4.6L SOHC V8
-
225 Horsepower (NOT 215) / 290 Torque I believe

- Older, bubble type body style
- Gas Mileage (almost the same as the 99)
- 1/4 time in about 14.7 guestimated

I had a 98GT, but never brought it to the track...wasn't stock either...
99 Mustang GT (specs from ford)
- 4.6L SOHC V8 (9:38:1 Compression)
- 260 Horsepower @ 5250 RPM (Has PI or Power Improved Heads that the 98 Didn't have, which gives the 35 more hp).
- 302 Torque @ 4000 RPM
- Newer body style (fender flares, etc)
- Gas Milage: V8 auto = 17 city/24 hywy, V8 manual = 18 city/26 hywy
- 1/4 time in 14.6 (from ford's page) more like 14.1 i'd say
- 0-60mph in 6.0 seconds (according to ford)
Good Websites to get aftermarket interior stuff for the stang:
www.uprproducts.com
--> Their Interior Stuff:
http://www.uprproducts.com/dynamic_index_menu.asp?v=mustang&m=MI
www.steeda.com
www.ageclassics.com
www.50resto.com
www.mgwltd.com
EDIT: I used to own a 98GT automatic and now traded that in for my 2002 GT 5spd. And i loved the swap

My 98GT had exhaust, gears, and other goodies, and it still isn't as fast as my stock 02 GT now

Get a 99+ 5spd. I think the 99+ look better anyway, but thats a toss up for some
EDIT #2: The Insurance is another thing. The insurance change from my 98GT (in new jersey) was $2400 (no collision) for the year. Now it is $2800 (no collision) for the year. So the jump wasn't that bad, considering my new car is 4 years newer. Just an FYI and a heads up. Jersey also has some of the worst insurance, so...