Hi Jon
I did wonder whether to remove the valve gear - especially after seeing it on the video. Might give it a try to see what it looks like. Does seem a pity to lose it though.
Yes, the side tanks were designed specifically to hold the 18650 batteries. I thought of putting the soundcard in the boiler in the space originally taken by the Stainz circuit-board, but the two pots for volume and tempo would be inaccessible. If I'm feeling brave (or reckless), I could remove the pots and replace them with pots on flying leads.
A bit disappointed with the soundcard, especially when the 'new' price is considered. Bought it on eBay quite cheaply so not too much out of pocket. Unlike the MyLocoSound card, the tempo increases in distinct steps - very unprototypical. The chuff is a bit synthy as well though the whistle is a lot better than the MLS (if not particularly UKish). At least it's better than the sandpaper-rasp of the old Stainz card.
Rik