I've dumped quite a few new RX-78 games and sent them to SSJ to get added to MAME but there's two I am unable to run as they are 32KB instead of 16KB. I am wondering if its because the emulator address space doesn't go that high when loading the ROM? I've put the ROMs here if somebody wants to try to mess with them. I only tried them on Takeda's emulator so far and not MAME. I believe they're both good dumps but I can try to redump them if someone thinks they are no good.
The motocross one is actually two 16KB chips on one board, only one like that. But you can see a pinout and a picture from a blog post someone did about it here - https://re-enthused.com/hardware/rx-78-cartridge-information/
Sekigahara I got to boot to the title screen by taking the first moving the first 8K of the ROM to the end of it but the logo of the game doesn't seem to load and i can't get it to do anything. According to the manual space bar should start the game, I think it also oddly uses the 2nd controller port instead of the 1st maybe.
You can get the two 32KB dumps here - https://www.gamingalexandria.com/rx78/
Also just added a tape dump to that folder. I haven't gotten it to work in Takeda's emulator yet though, maybe it will in MAME? You need to load the BASIC cart first then type -