I understand all two speed rear axle trucks have the adapter. It is strictly mechanical no vac invloved.
If the speed-o-meter cable went stright into the speed-o-meter gage, then the adapter was missing. It screws right into the back of the speed-o-meter gage where you found the cable attached. Imagine where the cable meets gage, the adapter fits there between the cable and gage rear...
If there was no adapter inplace, it is likely you do not have the piece of hard wire that attaches to the two speed axle switch/dial that mechanicly changes the rato in the adapter on the back of the speed-o-meter. It is just mechanical flip of a lever on the adapter. I'll try to find you a picture.
