Did you see this thread? https://ogrforum.com/d...ent/4245430038641974
From comments in the thread, the tender is reasonably large, so I can't see any reason the PS/2 3V board set and speaker won't fit into it, it's pretty compact. The biggest issue will be fitting the tether between the engine and tender neatly I would imagine.
I stuffed the PS/2 upgrade into the MTH General, which has a lot smaller tender.