1) That's an interesting speculation, and would make sense historically, since the Germanic tribes who settled in Britain seem to have absorbed more than a little from the Celtic peoples they conquered -- the fact that Old English images of Thunor show him with a sword rather than a hammer is one indication here. (I suspect he was conflated with Lugos, who wielded a sword.)

2) I'm sorry to say I'm not familiar with one. I'm still piecing together the rest of the system in which the solar plexus exercise has an important basic role!