Read this thread. Just about everything said there about bodies addresses your first question.

If I were building one today, I would use N&N. If price is no object, then Wescott.

Laminating metal onto a 33/34 firewall strikes me as a pretty serious chore. The shape of the firewall is very complex.

I don't think you're going to notice a power difference among the rear axles you mentioned. If you're going for the look - quick change. Otherwise, 9".