Thats a WHOLE lot of miles on your motor too start putting a S/C on it. IMO. Give Joe a call at MUSTANG MAGIC and ask for his advice.
http://www.mustangmagic.com
It only has 108k, thats not high really these days. And mileage is not a huge deal with these cars if they are taken care of. I've seen 20k mile Mustangs blow up, and personally have a friend with 175K+ in a SC'ed Mustang that runs 12.48@111 with stock T-5 and all.

Maintenance is the most important thing.
Do a compression test and a leak down test if you want to be sure of the engine condition and as long as the car has a nice safe tune you will be fine. The Mustangs I have seen blow up were either a bad tune, pushed WAY too far, or not taken care of. Mileage is not the best judge of a car or an engines condition.