OK, lets get this one sorted. The type I was looking for as the Faucett F-19, sometimes known as the Stinson-Faucett F-19. Built by Faucett Airlines of Peru over the period 1934-1946, there were a total of 36 which were pretty much copies of the Stinson SM-1 Detroiter - the type which was so successful that it enabled Stinson to raise the capital to become a public corporation.
Faucett modified the design in a number of ways, including upping the passenger capacity from 6 to 8, building all cargo versions and amphibians. Some of the aircraft eventually passed from Faucett to the Peruvian Air Force in whose museum the sole survivor - a cargo aircraft preserved by Faucett on a plinth outside their HQ at Lima, until their demise in 1997 - now resides. This aircraft msn 29 is painted to represent msn 8 which performed the first nonstop Lima o Buenos Aires flight.
The clues relating to the type number referto the ommission of type number F-19 from the USAF inventory - something which has led to much speculation regarding an unannounced "black" programme.
Finally the very tenuous link between the Barkley-Grow T8P-1 guess and the F-19 is that a T8P-1 made a record breaking flight from Washington DC to Lima.
Back shortly with another teaser - easier this time I promise.