2001 cobra seats fit in a 98 GT?

yes

Fronts - yes.

Rears - if the Cobra is a coupe then no. If it's a convertible, then yes.

I would HIGHLY recommend that he make sure the seats are in good condition otherwise don't do it because I got some for my GT 3 years ago and the leather was worn and I figured I would get it fixed....well my only options are getting all new seat skins for $900 and then paying another $300-$400 to get them put on the seats from an upholstery shop.

I would have rather waited and found a mint set of 03-04 cobra seats....