It seems to be a JA2-2, the newer type. These are Chinese 15 clones, the newer ones have reverse and droppable feed-dogs, apparently. Problem is googling gets me a cubic buttload of Chinese distributors, but no actual info from people using them. The one I've been offered is free but far away, so I'll have to accept it without trying it first (and pay for shipping).
I don't want to adopt a poorly working machine, and "made in China" isn't a real stamp of quality, sadly, so I was hoping for some input from an actual user.
The reason I am even considering saying yes is it's so pretty and it would be lovely for my daughter to learn on one of these years, because treadles go nice and slow.