[TJR]

Well, I doubt your going to get the Mustang to sound like the big block. In my opinion though, nothing sounds better than a 5.0 Mustang with 2 chamber flowmasters (keep in mind that I've been around a lot of purpose built race cars and street cars).

I would get a set of 1 5/8" unequal shorties, 2 1/2" off road H-pipe, and a set of (2 1/2") two chamber flowmasters. From what I've heard, this setup sounds the best. Also, I would not waste the money on the equal length shorties. They're more of pain to work with (especially when changing the plugs), and the gains with them over the unequal length are minimal.

As far as the computer and no catatlytic converters goes, it's different for every car. On some cars, the O2 sensors have trouble sampling the air since the restriction that was once there is now gone. Also, It might cause the check engine light to come on periodically, and you may experience some lean poping every now and again. To avoid this, you could weld some metal tabs behind the 02 sensors (inside of the h-pipe to slow the exhaust stream) or you could get an H-pipe with high flow cats, which will quiet down the exhaust a little bit. That's my $.02 on the subject.