I have a spare copal 1 shutter kicking around. I was looking around surplusshed.com and they have several different positive menisci and achromatic menisci that would just fit inside the rear threads of the shutter. Convenient and cheap, about $8 each.
Is there anything I should know about spacing between a meniscus lens and its stop or should I just stick a lens in there and not worry about it since choosing a meniscus does indicate that optical flaws are desired?
The traditional way to use a meniscus is to have the concave side towards the scene (away from the film) with a stop an inch or two out in front.
If you move the stop you change where off-axis rays pass through the lens. You trade off the geometry of the projected image (distortion, field curvature) with off-axis focus and blur/bokeh (especially the 'ugly' asymmetric aberrations like coma and astigmatism). The principle is easy to understand: with the aperture stop right next to the glass a ray coming in from an off-axis angle will still pass through the same central part of the lens as an on-axis ray. Move the aperture stop forward, and the off-axis ray passes through the glass at a point which is increasingly moved away from the centre. Aberrations like coma and spherical aberration come from the different focus achieved by on-axis and off-axis parts of the lens, so as you move the stop forward you get higher contributions from those errors.
In practice, it is usually easier to tinker and see what kind of image you get on the ground glass than to run an existing meniscus through an optical design program. This is especially true if you are after cool and froody bokeh effects. Without specialist equipment it is hard to measure the shape and optical density of a loose lens to high enough accuracy to make the calculations worthwhile. If you can make a cardboard tube telescope or independently support the lens behind the shutter in some way you can move it around and see what kind of effects you generate.
Note however, that you should check the 'look' you get on the ground glass, or better, with a piece of film or a paper negative. It is surprisingly easy to make the pupil of your eye part of the overall optical system, which can radically alter things like distortion and other aspects of image geometry, as well as bokeh.
A good starting point would be putting the stop 1/5 of the focal length ahead of the meniscus, concave side towards the subject as Struan says. In ideal circumstances that would give you 20-30 degrees of reasonably flat field. With a found lens it's unlikely to be even that much. There will still be plenty of softness and blurred borders, believe me.
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