I did a little research and it seems that you can control your EFI system on the fly and its relatively cheap! Cheaper than a scan tool even. Well that all depends, we're not counting the price of the computer here. What you need is a computer with a serial port, and thats about it. Today you can probably pick one up for $1-200 if you scan the newspapers. Then go check out http://www.customefis.com/winaldl.html and its links for all the info you need. There they have a free program to use on your laptop to view everything and http://www.akmcables.com/ carries the cable you need to connect for $95. So if you already have a laptop with a serial port $95 gets you in business. Neat huh? Only problem aparently this only works on 1986-88 3.8 SFI '3' LG3 1986-91 3.8 SFI '7' LC2
1986-87 3.8 SFI 'B' LG2 . But alas there is lots of other software out there for GM OBDI. Oh and yes they do sell connectors for OBDII but its on you to find the software at a reasonable price. How cool would a laptop controlled ECM be? I might look into this further

Doc, Turtle_sse built a custom standalone fuel management system already. You may try to email him for details. If you have trouble getting ahold of him, let me know. I'll track him down for ya!