I needed to downgrade the firmware to version 5. It seems from version 6 and up, developer Krikz changed the video mode slightly, and the game select menu no longer works on a Mark III or other non-Master System hardware (e.g. a Game Gear in Game Gear mode via a modified converter).
However, the combined cart/converter was a long way from fitting into a regular Mark III cartridge shell. First of all, the SD card sticks out. A lot.
I looked around for a micro sd card adapter that would work, but a couple I got didn’t fit, or were not low profile enough. Then I came across this.
You can simply cut many SD cards in half! Sure enough, the 2GB SD I was using was empty in the top 2/3, so I sliced off the excess plastic.
And now it sat well clear of the edge. This became very important later on, as I needed that extra few millimetres of clearence.
Next I had to open up the shell I was going to use. A $7 copy of Space Harrier from eBay was my sacrificial lamb. To open Mark III carts you have to access some screws under the label, so I used a hairdryer to warm up the label glue, then a pin to start peeling the label.
It’s fairly easy this way, with no damage to the label or cart.
After getting inside, I sliced away all excess plastic, but the combined cart/converter was still sticking well out the bottom of the shell.
I gained a couple of millimetres by shaving down the top plastic rim
But the real gains would be had by filing/sanding back the contact pins on both the flash cart and the adapter. Contact pins are far longer than they need to be, they really only need 1-2mm – just enough to make a solid connection. Wear and tear is much less of an issue than back in the day, as I won’t be inserting and removing the flash cart from the adapter ever again, and the whole unit itself will stay in the console for most of the rest of its life. So I brought them down to about half their original height.
And now it’s going to sit just 3-4mm higher than a regular cart would! I could have gone further, but wasn’t going to push it too far and risk damaging the flash cart or adapter beyond repair.
Next up I had to brace the combined cart inside the shell. I superglued some plastic from a damaged SNES controller in, braced against the bottom of the cart shell, and backed it with hot glue for support from the sides.
It slots in under the adapter’s slot section, and I have a snug but secure brace for the board!
Close up the cart for the finished product! It sits slightly higher than a regular cart, but low enough to be quite stable within the cart slot, as it still sinks into the slot about 10mm. It sits lower than an unplugged cart resting on the cart slot, for example. At a glance you can’t even tell.