Before the Treaty of the Americas and 911, I ordered a CVA kit from Dixie, and simply showed my FAC at the post office and picked it up.
I think it depends if the US restrictions against selling to non-resident aliens applies to ML's as well as centre fires. I believe that the US regulations on ML's are different than CF's (I think they can buy them by mail order). If this is the case with non-resident sales, I think the advice you received before may be accurate. I think if you present a gun at the border with a PAL, you would be allowed to import it (subjuect to the payment of all duties and taxes). I don't know how they handle the registration issue.