I bought a vogatek MK. III supergun a few years back. extremely easy to set up, just buy PC PSU (preferrably one that has -5v), wire the controllers and youre all set. you can use external speakers, but seeing as how theres a headphone jack, you can figure out how to output on your TV speakers. the s-video puts out a super clean image as well. you might want to invest in a JAMMA extender if you dont want to plug the PCB into the supergun itself.
as for an enclosure, i bought a rather large one - it accommodates all of the components, and its big enough where i can put some of my larger PCBs on top without fear of falling or worrying about where to put them while im playing