[blue00gt]

Since when do longtubes do very little on a near stock mod motor? I have BBK longtubes and catted h-pipe on my 2000 GT with very little else and I can hang dead even with my buddy's '99 Cobra until over 100mph. Shorties will get you nothing - maybe 2-3 hp at most and are not even worth the time they take to install. If you decided to get shorties you might as well leave the stock exhaust manifolds on and just get a new mid-pipe.
As far as BBK goes, I am not happy at all with the fit of my longtubes and I am looking at other brands to replace them. At around 2K rpm at certain throttle levels the passenger side header taps the frame. The matching BBK h-pipe also mates up to the header collectors like crap and I had a hard time bolting it up without an exhaust leak there. I'd stay away from MAC longtubes also. Hooker also makes longtubes for the mod cars but I have had no experience with them. Bassani just released a 'mid-length' header that looks interesting.
As for install cost I did it myself and it took me over 10 hours; not sure what a shop would quote you for labor.