What about the 404 on the Argentine? That is a nice combination.

I applaud your dedication to historical authenticity. That's the view/affliction I have in rifle building too. I don't even like modern scopes!

I believe the LW barrel would be excellent as it is. For a 404 I can't imagine I'd want to make the barrel any lighter than .625 at the muzzle, even if the original was a tad lighter, but that's just me. Will you be trying to reproduce the contour precisely in every dimension?

Another interesting thing about the LW barrel is the straight section in front of the radius at the breech - very handy for mounting the sight base/recoil lug fittings Recknagel sells, but did the original rifle have that feature? It's .865 in diameter, and several of the Recknagel lug/sight base fittings are .866 inner diameter. Obviously they're meant to be together.