I would say that the most daunting task in building a supergun is taking care of the extra 3 buttons for fighting games. If I were to build another I would include terminals for --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type--,B5,B6 and ground on the supergun for player 1 and 2. This way the extra kick harnesses could be tied into the supergun with minimal work. Superguns seem to be built by alot of people who want fighting games and this would accomodate the extra buttons that the Jamma harness does not. -5V should also be wired to the jamma harness as it is required for some games and will not bother games that do not require it. A PS that provides a visual indication of the 5V would also be helpful since the 5V must be adjusted for some games. This can be provided on the arcade PS or test points can be added to tie in a DVM.
It is hard to draw the line between a supergun and a fully optioned jamma test fixture so the meter is probably not required for most fan type superguns.
The addition of a RGB to NTSC or PAL converter is critical for anyone who wants to use their TV as a display. JROK's units are very good for this conversion.
Hope that helps
BobA