A brief semi-related follow-up for anyone who's interested. When I got the aforementioned Brownie Hawkeye, I also picked up a Brownie Flash Six-20; the latter camera is, it turns out, far easier to convert to pinhole. By simply prying the lens off the front (held on by three small tabs), one can afix a pinhole plate directly over the aperture/shutter. The shutter has a B setting, and the camera even has a tripod socket already. All I need to do is drill the top plate to accept a cable release and it will be ready to go.