http://www.tunercat.com/index.html
He has a LOT of the GM stuff covered. Take a look around.
That is what I use to tune my car, tho according to the dimwitt jcat I have probably just screwed everything up doing so.
I would be surprised if an 83 had a speed limiter though. I had boxies before the current pair of a 94 wagon and the 96 sedan, never played with them much though, just transportation.