One of the Brownells Gunsmith Kinks books has a hand drawn picture or two of nitro special hammer installation jigs. One fairly simple method involved clamping the action in a padded vise on a drill press table and pushing the hammer in place with a chucked up block of sorts that cradled the hammer. I would imagine an arbor press would work as well. I the books also show one that is a uniquely C-shaped hand held tool that was specifically made to install these hammers. Ill try to find some pictures if possible.
