Assuming the C39 you are starting with is a pistol there is no legislation that I am aware of, state or federal, that restricts you from shortening the barrel or replacing the barrel with a shorter one. I'm not familiar with the CAI C39's. One search I did produced a link to a rifle at...
Under last year's regulation change does just the RP need finger print and photo for new (post 7/16) NFA item applications or does the Successor (or Beneficiary) also need to submit prints and photo on any new trust items? I was told "everyone on the trust" must do photo and print.
I just did one. Cut the notch for the hinge, drilled the rivet and bottom holes as well. The hinge notch I marked off of the hinge location when inserted into the receiver, up to contact. I did the cuts with a dremel wheel and grinder bit on the conservative side, then file to fit. Works well.
I have. That's a good tutorial. I just skimmed it but it mentions a half of a thousandth interference/press fit (.0005"). That is not much at all. The critical factor is supporting the receiver/trunion. That is a must. The listed tool is ideal but you could probably fabricate something to...
I have a press and could help press the barrel into the receiver and possibly help with headspace. But, I've never built a VZ so could only help try and figure it out. I have a VZ for reference as well. I'm not a gunsmith either, I should add.
For trees I'm not wanting to do myself, I use Arundel Tree Service. They've done over a dozen trees for me. Good prices. They have a boom/bucket truck as well as the standard chippers and will also climb and cut, etc.