Looking to build a 45/70 on a P14 Enfield action in WA State

Probably a strange second post for a tactical rifle forum...
So, I have been dreaming about building a 45/70 on a P14 Enfield action. It would have a 16.25" BBL, a sporterized military stock, aperture sights, a threaded muzzle, and a Kaw Valley Precision linear .458 compensator. All the metal parts will be parkerised. I would like to be able to feed it with stripper clips.

I have a couple questions. Where is the best place to purchase a BBL? I am looking for a hunting weight barrel, not target weight. Where should I have the barrel threaded, and installed? I plan to do the rest of the work myself. How much should I plan to spend on the barrel, having the muzzle threaded, and having it installed on the action?