You should have the electrical switch to the left of the steering column. The commission plate on the firewall will be stamped with "LO" at the end. Both of those tell you the car originally had the OD. The verification that it is still there would be to look under the car...the OD has a large drain plug behind the tranny that is very visible. If you can't get under the car, then look for which side the speedo cable originates. If it comes up on the left, it is a non-OD. If it comes up on the right and crosses the firewall under the battery box, then it is an OD tranny.