The Clack is also very stable. Sort of like a babushka of a camera without the head scarf. Anyway, here is a page that details the conversion process. Worth a read so you don't yank the wrong thing. I think the directions should work for the Click as well. No "B" shutter though, unless your click is different from mine, but removing the light weight return spring on the shutter might give that effectively. And you can always just remove the entire shutter assembly and use a snug fitting cap as the shutter.
http://kosara.net/photo/lochlomo.htmlAnd as far as the pinholes go, I spent actual money on mine. Pinhole resource sells the set I got, and they sell individual sizes as well.
http://pinholeresource.com/If you are steady with a needle, you can make one out of aluminum foil. Sam made a pinhole camera from cardboard and a Polaroid back using a tinfoil pinhole that was nearly as sharp as my commercial pinholes. There are a lot of pinholes in a roll of Reynolds Wrap!

Good luck!