You can check out the NMRA site for the Factory Stock rules (www.nmraracing.com). I haven't read through the FS rules lately, but they are pretty strict on what can be done and in what combinations. You could also post to the NMRA message board to discuss your combination with some of the other FS racers. Joffre LaFontaine seems to be leading the FS pack with times in the 12.90's , I believe.
As far as the T5 goes, you can get a brand new WC T5 from D&D performance (in Michigan) for about $799 which is a good deal. I've bought one from them myself. Or you can find a used one and rebuild it yourself. Upgrade to the WC gear clusters and blocker rings, steel bearing retainer and definitely get a good shifter (Pro 5.0) on it so that you don't bend the slider and shift forks. Check both the slider and forks if you pick up a used tranny...they're often bent if used hard with a stock shift.
Hope this helps.
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Jeff Chambers
T/S #4
12.028 Seconds/114.51 MPH
http://www.kellnet.com/chambers/default.htm