I wondered about the UPF6 as that wasn't one I recognized off hand. As to NC13427, it is hangared in Wapato Washington and is now owned by Greg Babcock who is an AI & A&E and he and I talk back and forth occasionally and verbally I am supposed to have right of first refusal if and when Greg decides to sell. He still has all of the original logs and the plane is still in current license and flown by him as needed or wanted. I have pictures of my oldest boy, Mike, setting in the plane when he went back to the state of Washington on a trip and made the effort to go see his grandads first plane which I think is neat. I will scan some and post later.
HD - would love to see the pictures. I would guess that a Waco was a pretty ritzy plane in general in the 1930s, unless someone had the dough for a Spartan Executive or one of those other 450 horse sized planes.
I did check the number of registered VPF-7s, and there are a total of two registered in the United States, so there may be some truth to it that only 6 were produced. There's some scribble or tags or something in the plane, too, signifying its use in Argentina's Air Force. I guess being a rare Waco isn't that rare, though - seems like when you look through the model line-up, there aren't that many that were produced in large numbers. Just about all them from the '30s and '40s are pretty. Good luck with your venture in getting yours back.