I have opened this up and have verified that it has 512MB in it (2x256MB). I also switched the jumpers on the NET DIMM board from GD-ROM to NETWORK and have verified that the networking menu now displays in test mode. I've not yet tinkered with networking, so am not sure how to otherwise test this.
I would also be interested in trading straight up for either a Capcom I/O adapter or Sega deluxe JAMMA I/O adapter (the one in the black box) with all of the cables.