1994 Chevy S1 turns over but won't go

Does it have spark? Very common to have an ignition module failure on these.

You should find a different mechanic that trouble shoots the problem instead of just guessing , You say it " turns over " does that mean it idles or does that mean it cranks ? Look for a good motor to chassis ground , spray some carb cleaner down the throttle .

That's true, shops only want to work on second generation OBD systems. An independent shop is your only hope these days in find someone that knows about the older systems. Unfortunately the good Techs from that era are retiring, some are keeping their hand in by doing driveway work at their home. As that is what I did for a few years after retiring. Now I only work on my own stuff.