By adding the dark blue frame decalled version to my turquoise frame decalled example of this Esso tanker, I managed to finally complete the Studebaker Tanker series! Some may have to be replaced by better examples in the course of time, but I am very happy now with the present eight various tankers. The box is dual numbered and the rear is without a '20' sign.
I am still uncertain about the periods of production of each of the two versions. Any ideas? Kind regards, Jan