Thanks guys
What we've got here is a bit different than any other high score or mod kit. I needed the board to be able to pull off a bunch of tricks - save high scores, save settings, play the original DK ROMs, also play the add-on Remix ROMs, also add high scores *and* the ability to switch back to Remix when running original unmodified DK ROMs, switch between multiple sets of add-on ROMs (the menu is a separate ROM)...etc..
That would have been a lot of hardware on the board.
So this thing is doing something different. The surface mount chip is a microcontroller and it has the high score and settings memory in it, also the binaries for the boot menu, DK Remix and optionally DK Deranged or even more versions of DK. It's running it's own program code too while DK's Z80 is running DK or whatnot. The microcontroller emulates Z80 ROM when it's running Remix. While normal DK is running, the microcontroller monitors what the Z80 is up to and intercepts when the scores and settings are loaded or saved, even monitors the control panel buttons so it could pull off things like switching between DK and DK Remix. That means the Z80 can be running unmodified DK ROMs yet we can still have extra features like high score save.
The other 3 chips are some glue circuitry to interface the Z80 and the microcontroller together.
It's brilliant. As far as I know, it's never been done before... and I'm taking a big risk doing it because it's never been done before.
If it works brilliantly, it's probable other people's future high score kits are going to copy the concept, maybe even other kinds of arcade, retro gaming or computing projects as well. We shall see. It'll be interesting.