The MAF mod was responsible for at least 15 of the 20 horses I gained, and the exhaust the other 5.
Remember it's still a 2.5" exhaust on a 3.0L engine
If you were to compare to the stock HP curve, they're equal until about 3000rpm, and then mine starts gaining bigtime.
The brass fitting that went to the engine block was 1/2 I think, maybe 3/8. Don't remember unfortunately

You can get the connectors/adapters/etc at Napa (where I got mine), and you should be able to get them at Pep Boys as well. Make sure you use some silicone tape (like for water pipes), else it WILL leak.
Main rig: Intel e2140 @ 3.0ghz, Asus P5K-E, 2x1gb Kingmax 1066mhz, 36gb 15k Fujitsu MAU, 500gb Maxline Pro,
250gb WD SE, Sapphire X1950GT 256mb, Pioneer DVR-111D, Pioneer DVR-107D, Antec TP v2.0 480w, Inwin q500n.
1995 Saturn SW2 - 15.3 @ 90mph:
http://www.sounddomain.com/ride/2346787/