Kal, putting a large ACME or ILEX shutter on the front or back is fine and like you said, the larger the better to avoid vignetting. Also, ND filters will become your friend! What I did when mounting my packard onto my petzvals was gaffa tape a Cokin P filter holder on the front. It's helped immensely as I only have the one shutter speed with the Packard when using in auto mode. I would love a larger shutter to give me more control, but not sure I have lenses suitable for shutters other than a packard.