What Universal X-pipe kits are good?
One thing I haven't heard addressed here is transmission/linkage clearance. If you are racing, you'll prolly have the tranny in/out b4 long. If you go the "custom" route, then you might want to keep that in mind.
Either make sure the collectors are bolted, so it drops down and/or that the "X" is far enough back to clear the tranny (or at least behind the pan/under the tail shaft...maybe someone with a 727 can chime in).
The shop will take the "easy" path (of less resistance), so make sure you explain you wants. Also (IMHO), with 3", they're prolly gonna spend a lot of time getting clearances up/over the rear end. My 2.5" was close in a lot of spots (shocks/gas tank etc.)
BTW, I just did Doug's/Pypes. Very happy with the results. It a '68 GTS 4 spd, so I was concerned if I needed to do a clutch. The Pypes "X" is (seems) far enough back to clear dropping the tranny (but I'd most likely need to unbolt the collectors).
When I bought my car, it had Hookers and a "stock" like system. No "H" or "X" pipe. IMHO I really think these help the engine breath better. Also gives a very different tone. You can check 'em on You Tube.
Pete