Mayhew all the way. Several of the other brands mentioned in this post are made by them (not only punches, but chisels and pry bars as well), and made in USA.
Do the joists run front to back, or did i look at the pictures wrong? If yes, then the joists aren't tied to the rafters to begin with, so its only the gussets on the rafter joints and their connection to the top plate that is keeping them from going outwards.
no idea what impact would be of...