ive used megasquirt on about 7 projects
it is very versital and very programable
once you get the electronics figured out and setup, tuning is a fun task
take your time and go easy on it. get a good wideband a/f meter and keep it in the 13-1 a/f for a while and tune it up to 14.5 max. (only go above that when you are REAL good at tuning)
i was thinking about using the gm tb on my buddys 66 f100 because its pretty easy to get it onto the stock intake.
im tempted to run dual 454 tbi units on the 390 in my mustang

its been a while since i ran one of my ms project, but if you have any questions ill be more then happy to pass along my experiances