Yea, sure. An STGW 57 barrel can be easily sold for $5k+ on the open market.
Out of curiosity, what would somebody in the gun control paradise of California do with a devil built, grenade ring machined, flash hider equipped, rifle barrel?
Law enforcement agencies would do non-taxable Form-5s to do transfers. The AC-556s are fully transferrable as long as they were manufactured prior to May 15, 1986. It appears these ACs can be transferred to private citizens.
A Mini-14 stock will not fit an AC-556. A Mini-14 stock needs to be milled out slightly to allow an AC-556 to fit in it. Back in the day, M60 Joe did this stock machining. I don't know who does it today.
Josh; Have you ever seen the SIG tool used to remove the old buttpad? I have heard of such a tool, but I have never seen one. I'm sure if a picture of the tool is published someone here in the US can make one.
USPS Registered and Insured. Have a local FFL take it to the Post Office with you. Have him do the shipping and you reimburse him for the postage and his service.