I've been trying to figure out which medium format camera to buy used to modify for pinhole photography. Not knowing much about these cameras, I thought I'd ask for some advice.

Here's my wish list: 120 roll film, possibly 6x9 or multiple size options. An interchangeable lens would be nice, which could easily be removed and replaced with a pinhole body cap. A viewfinder that's separate from the lens - twin lens or other system; some of the folding cameras have a metal viewfinder mounted on top. A "bulb" setting or other means of holding the shutter open longer. Also nice might be an interchangeable film back that accepts Polaroid (like the Mamiya 67RB), but it looks like that option starts adding $$.

Cheap would be good of course! I ran across an interesting old medium format, folding Russian camera, the Moskva 2, on eBay for about $30. It has a separate viewfinder, but I can't tell if the lens is removeable.

Any recommendations or experiences you've had appreciated!