The MS3Pro appears to have a good set of features on paper, but I have never been impressed with any of the megasquirt products I have used.
Have you looked at the Haltech units? Depending on what features you want, it might be a better option for you.
Do you know what you want to do for ignition? The Haltech supports drive-by-wire where the MS3Pro doesn't, but with what you have there going cable throttle probably makes more sense.
The Haltech can control a 4L60e and a few other transmissions if you decide on a modern automatic. The Haltech also supports closed loop automatic tuning. Whether that is a bonus or not depends on you.
