I was finally able to drive the pin out of my 27-3; I looked on both sides of the shaft for the more recessed end of the pin, and spent several days dropping a bit of penetrating oil (B'laster brand) so that it soaked into the area around the pin. I actually ended up drilling a bit away from one end of the pin (having read that the taper pins are typically made of softer metal) and that showed me that the end I thought was larger was in fact smaller. Driving it out the correct way is of course essential.
As for removing the handwheel collar from the main shaft once you have the pin driven out, this tool from the Featherweight Shop was absolutely essential:
https://singer-featherweight.com/pro...collar-remover
They were able to make it for me with a handwheel nut that I confirmed would fit Singer 15, 27, and 66.