Where are all the o2 sensors located? How many does it have? Add details if necessary please.

Did. Only found 1 in front of cat

It is NOT OBDII , so that is IT.

Awesome. To clarify: So The OBD1 version of my van only has 1 O2 sensor? Located before the cat?

Yes , OBDI does not monitor the cat function , and that is all the secondary sensors do.