posi rear end ?
If you car is still stock, then no, sorry. The V6 Mustangs in '98 came with a 7.5" open differnential. Only the V8 or GT cars came with an 8.8" rear differential with a trac-Loc or limited slip. Positraction is 2 wheels spinning at the same speed, limit slip would put power to either wheel, but closer to 2 wheel traction. An open differential is only one wheel will spin to deliver the power to the road. You can purchase a trac-loc for your differential and install it in place of the open differential.
Tom is 100% correct
Thanks guys, I wasn't sure and had a couple different friends telling me different.
Looking for a Used Mustang in your area?
CarGurus has 47,365 nationwide Mustang listings starting at $1,999.
Search Ford Mustang Questions
Ford Mustang Experts