Just keep the boost low (8lbs max) and you should be okay. I'd still run a compression test, and a leakdown test to make sure your rings and valve guides are okay. Because once you put on a blower, any small problem you might have is gonna be compounded tenfold.
If you're looking for used blowers, just look on eBay, and all the classified sections of the mustang forums. Stangnet, Corral, Hardcore50 etc. etc.
If you're looking for new blowers, superchargersonline.com has the cheapest prices I've ever seen.