that is what mine looked like too before it broke off
it was just a friction latch ..
a few years ago i had a 3x4 rb that i sold soon after i got it
the front door latch was very different, as you described ..
the pin was retracted into the body until the bellows were fully retracted
and then it popped up and poked into a little hole on a piece of metal that
stuck out from under the door


for my bag mag repair
i removed the bag carfuly from the box
and found someone who is a tailor that repairs leather goods.
he knew how to repair and make a new bag, and did what
he called a "light proof stitch" it was done in 95 or so
and still works great!

i think it cost me about 30$ ...
if you have the tshirts and leather lying around
that will save you the $30

have fun!