$350!! That's about 175 quid for an AW cab. Lucky git.

Anyway... I can't see a JAMMA loom in there anywhere. What are the button and sticks wired to; an I/O board? I can see what looks like the JVS power connectors. As for the monitor, if it's a Toshiba trisync from an E3, you've done well. I'm not sure if the monitor accepts all signals through the VGA cable, or if it has a separate input for CGA signals.

If you want to run JAMMA & MVS I'd suggest removing the JVS PSU and putting a normal arcade PSU in there. You'll then just need to hook everything up to a JAMMA harness and you'll be good to go.

If you want to run a Naomi cart system in there then a Naomi MoBo with a Capcom I/O is nice and easy to set-up. You'll be able to plug the JAMMA harness straight on to the Capcom I/O. If you decide you want to run a GD-ROM system in there get a Dreamcast, it's a million times easier and a lot cheaper.