A little while back muddymusic lent me his PCE-JAMMA unit to look at.
The whole saga can be found here.
There is pretty much no documentation available out there for this unit but my friend Tormod seems to have quite a bit. Here is a scan of the manual he has for it
After tracing the hardware out and various trials and a fair amount of input from the arcade community we came up with this:
Its not a bad system really and it works well for what it is