I have an old milsurp Mauser.  

I took it out of the military stock, and bought a Fajen.  Well after hours and hours of sanding and inletting...i find that the holes for the action screws were never drilled right so it will be a major PITA to move the action/barrel back to line up with the bottom metal.  I still might do that.

Anyway, if I took 2 pieces of square tube stock, and put clamped them between the bottom metal and the barreled action, and then just hung a shotgun forearm (free floated [;) ) off the front of those, and rigged up something to stick a buttstock on, would that work?  Like threaded rod going from the buttstock, thru the 2 tube metal pieces, and into a shotgun foreend.  

Yes I'm that damn bored.