The PROM's in our generation vehicles aren't flashable like the newer stuff.
You've got to change a few things to screw with programming, and you can see all the stuff that is out there for OBD1 stuff (which is all GM until 1996) at moates.net
You can erase codes by removing the ECM fuse for 10 seconds. You can retrieve codes by jumpering terminals a and b on the connector with a paperclip. There is at least one ALDL pinout on the net, I think ours is a 10 pin connector, (rectangular, I know that much) and although there are other versions, all are foreign. Just need the pinout that matches the number of Pins our ALDL has.