First and foremost 'do your home work' on what a real Rubi has from the factory and how to identify it...particularly the gears. It is not hard to learn and this site has all the info if you do a little reading.
Mileage at 90K is no big deal if the rig has been cared for...again do some home work so you know what to look at.
If you are not an expert on aftermarket bits and pieces and their proper installation, then I would steer way clear of a mod'd up rig....the closer to factory that Rubi is the better off you'll be.
Do your home work before you get to serious...have fun and enjoy the process.
'98 Sport 4.0 - Auto, Hard/Soft tops, Dana 44's, 3.73's, Mostly stock...