A "shorty" header is a header designed to fit onto the stock y pipe for any particular vehicle, as opposed to a full length header which would have to be welded into your existing exhaust setup. "Shorty" headers are made by nearly all the big name companies ie. Borla, Bassani, Gibson, Heddman, etc. I know that for sure, Borla offers lifetime warranties on many of their headers, and i believe that Gibson does the same. I would just suggest that whatever you choose, go with something from one of the big exhaust companies and use high grade fasteners like ARP. That way you shouldn't have to worry about any bolts breaking.
As for taking off your old exhaust manifolds . . . soak the heck out of the bolts before trying to loosen them . . . so you don't strip or break the heads off. Anyhow, good luck.