Also worth noting:
Just because you have OBDI, doesnt mean you can't build an interface cable. In fact, OBDI cables are much easier to make then the OBDII varieties.
Here are some sites to get you started:
With OBDI, you cannot modify the way the engine runs without buying a chip emulator from moates.. This emulator adds the reflash capapbility to the older ECM's, which use UV eraseable PROM chips instead of flash chips.
However, for 15 dollars at radio shack, you can build a cable that will allow you to pull your error codes, see all sensor data, and observe the general operation of your engine.