When I correctly hooked up the dual stack PCB setups for Air Rescue and F1 Exhaust Note it was pointed out to me that GP Rider on the X-Board platform used a similar setup – a bridge board with shared RAM mapped directly into the address space of the main CPUs on each stack rather than a network.
In order to support this the driver (and several components used by the driver) required a little work in order to allow for multiple instances of the PCB stack to run under MAME at the same time.
I did this work, but the game still didn’t work correctly (the game would desync and break shortly after coining up), at that point I passed it on to SailorSat to look at and she observed that the RAM was actually banked, and once she hooked that up it started working as expected.
There’s no new fancy double screen attract graphics in this like Air Rescue and F1 Exhaust Note have, but there are a few things you won’t see unless you’re running the Twin setup either way. Note, I believe the Twin setup is the only official Sega configuration for this game, and while it can run with a single PCB stack that isn’t how it was designed to run.