Howdy Story,
With the trigger/half cock issue, that may make the conversion even more problematic (costly). In addition, the cylinder walls look awfully thin. All that being said, first I'd see what .32 ammo will chamber. Regarding firing pin hole, take a deprimed case and drill out the cavity to just allow a long punch to be centered, then use the chambered shell and punch to mark the breech face. That's where your hole needs to be. Maybe even a slim, fine point marker could also be used.
Them's my thoughts,
Rev. Chase