Here are some photos I took of Lockheed C-60 Lodestar (Lockheed Model 18) examples at March AFB, Planes of Fame and a fuselage section on display at the Pima Air Museum in Tucson, Ariz.
As war approached in 1940, Model 18 Lodestars airliners were impressed into the military as the C-56, while factory-built aircraft were the C-60 for the US Army and the R5O for the Navy/Marines.