For anyone else, location of OEM armrest mounting holes from my '93 parts car. Front seat was out of the car when the pics were taken. The OEM version has small flaps in the carpet hiding the mounting holes. Mounting hole for the rear end of the seat rail can be used as reference to location of arm rest.
The holes are not simply drilled/threaded in the bare sheet metal, the front hole has some kind of backing piece which is tapped, and the rear hole has an insert, both of which allow more than a couple threads.
The front hole lines up with the rear seat rail mounting hole. This is the third hole in the pics toward bottom of pic.
