with pre-OBD2 GM cars, it's pretty easy to get the computer to flash the codes. Check online as I believe you just need to short pins A & B and the codes will flash on that SES light.
You may have a failed or failing vehicle speed sensor, if this vehicle has one.
It seems the other engine choices were fuel injected (according to PartsAmerica.com) and there is a VSS listed for this vehicle, so it's reasonable that this is the code. But check to be sure.
HTH,
TB
