Opinions on this car

Looks like it was wel taken care of but SC'ed cars can always have some hidden stuff, depending on how well it was taken care of. For a 96 its relativly low miles if they are the correct mileage. You would have to check the vin to make sure its an actual saleen and not just a badged GT made to look like a saleen.
 
Price seems good, but he states it has a rebuilt title in Mass. The car may be fine, but there are enough Mustangs out there that I would likely steer clear of anything with a rebuilt title.
 
It depends. If the car is close, definitely go take it for a test drive on the freeway. You'll find out pretty fast if it has any glaring issues at 70 mph.

I've had a car totalled for having the front clip torn off in a low speed accident. Had it fixed and had no issues down the road. Whether a rebuilt title car is good or bad depends on the damage and the quality of work that went into fixing it.

My uncle bought a 98 Formula that had the entire front forward of the firewall replaced at a dealer body shop, and it was pretty much perfect. The frame was straight, the paint and body were probably better than stock, and the front struts/bushings & tie rods were all new. For the price he paid it was a great deal and had no issues over time.

But the resale will always be lower. A rebuilt car is worth less than a clean title for a reason.