Yeah, it was me.
I did a special build of MAME so people could play it, but it's a bit glitchy so I need to sort that.
It's not in real MAME as...
I did some initial Namco linkup code a few years ago and shared it on a forum, Sailorsat took that and made it better (more systems, more players) then submitted it to MAME... and it went down like a lead baloon, probably as it was a massive change with loads of other things thrown in so a nightmare to review.
Sailorsat broke it down into smaller submissions and was waiting for help/feedback, but that wasn't exactly overflowing and now they've gone quiet too.
I haven't got the time to get involved with all that, code reviews are bad enough in my job, never mind for a hobby, so I just did the triple screen as a standalone build. But it's using the same code that Sailorsat submitted and we both worked on. That's why I was a bit sniffy about the closed-source of this new emulator as I'd be very surprised if it isn't using the linkup stuff from sailorsat's CabMAME branch, amongst other things.