I just bought a matching lock set from LMC for my 55 S2 3100. Like your truck, mine only had a lock on the passenger door. To lock the truck you would have to lock the drivers door from the inside and then scoot out the passenger door and lock it from the outside. So far, I have only installed the lock on the drivers door and it just prevents the outside button from pushing down. This means that if the lever on the inside is in the locked position it will not unlock it. I have not gotten around to installing the new lock on the passenger side yet so I am not sure about how it will work. Be careful when ordering these parts. I live near LMC and the counter guys had to open 3 different kits before we found one where all the locks and keys matched and worked together.
