Converting a Vintage Box
If the box camera does not have a "T" function by pulling a tab, you will have to make it.
Pull off the front of the camera. It is held only by its two tabs that fit over two posts on the body and comes off easily Using a screwdriver gently under one tab, then the other. This is a good time to clean those viewing lenses and mirrors.
By working the shutter you will see that it is a disc with a slot in it that make a trip between to posts. We need to put an obstruction at about the 3 o'clock position to that it will work as a "Bulb".
Glue the obstruction around that spot being careful not to get any under the disc.
Find something to use as a post and drill a hole for it and glue the post in this hole so by using a rubber band it may act to hold the shutter release down.
Remove the lens. It is held by a "C" Spring which can be sprung with a small screwdriver.
First option (easiest) is to mount the pinhole where the lens was. However this will yield images with vignetting corners because of the distance from the shutter opening.
Best option (most difficult) is to mount the pinhole on the rear of the shutter opening. I did this by putting the glue in a toothpick and very carefully bringing it through the front of the open shutter and working the glue onto the inside edges of the opening. Then using a long pair of tweezers or needle nose bring the pinhole down inside the camera and drop it on the glue around the shutter hole. Tamp down the edges.
Here is a rubber band holding the shutter open.
Glue on a filter ring if you want.
And get yourself a fridge magnet to open and close the little red window so your can use 800 speed film if you want.
The following images were all captured this camera. The B&W were on Agfa APX 400. The color was Fuji NHGII 800 and Fuji 400.