U1300L Door Locks

I recently became the proud owner of a U1300L that started out life as a military troop carrier. I need to get a safety inspection done on it to keep my insurance company happy, and in preparation for drving it into town to work next week, and leaving it parked down town most of the day while I am at work I was going over securing all of the boxes, the spare tire, etc., and I noticed that I couldn't lock the cab doors with the ignition key (only key I got from the previous owner).

Can anyone confirm that the doors on the military U1300L came with lockable doors (there is a keyslot in the release button).

Can anyone advise if the ignition key should work to lock / unlock the cab doors, or if the door locks utilize a separate key.