I believe there is a gang ground on front of the left head, upper bolt that should have a bonding wire and 2 other wires connected to it.
If you install those two wires that are missing from the ALDL to the PCM you will be able to get codes out of it.
Not sure about the compatibility issues if you upgraded to a '97 computer setup. You would have to do some research about that one.
PCM swap for the LT1. All Stuff LT1 related