Well, since I used that camera with that bellows outside in direct sunlight to make an entire series of images for several months, I kind of doubt you're going to find any pinholes in it. Larger holes often put a second layer of image in the scene. The easiest way to check for pinholes is with a flashlight inside the bellows in a darkened room. In an indoor scene like this, I doubt you'd see pinholes anyway becasue of the light levels, but I suppose you could with such a long exposure.
As Dave asked, what are you looking for? To me the image looks flat and lacks shadow detail, which could be from the lens (or from my crappy laptop monitor....) Are you shooting onto paper? If so, you might need to filter the incoming light with a filter similar to what you'd use on your enlarger.
Also, it appears that you didn't have the back completely levelled as there seems to be some line convergence.
Cheers, Richard