bulgie thank you for the detailed response! I'm hoping to avoid having to install an extreme setback seat post, as it puts the stoker way out over the rear wheel. But, as you can see from the photo of a similar 3Rensho tandem, it has exactly that setup. In my case, I'm hoping my wife, who is about the same height as me, will be able to fit comfortably. I agree that a flat or very very slightly swept-back riser handle bar in the back is probably the best choice for the stoker.

Speaking of tire width, I'm toying with the idea of building this bike up with 650B wheels. I did some preliminary research and it seems do-able, although I will need to install a gizmo that lowers cantilevers a little bit. I'm not going to have a frame builder make any changes to the bike. Other than the canti posts, do I need to worry about the change in BB drop?