Morris, Franquin and 'Le Moustique'.

In the 1940's Morris, Franquin, Jijé and worked together at the same studio. in 1946 they even traveled to the US and Mexico together while working for Spirou magazine from overseas. Beside Spirou, Dupuis also published 'Le Moustique', a weekly TV and radio magazine that also had lot's of news and other informative articles.

The Belgian comic authors frequently created gags and covers for the magazine. Tilleux even published his comic 'César' in it from December 31, 1959 until July 28, 1966 and Morris also had two comics published in 1954, 'Lucky Luke and Phil Wire' ('Lucky Luke contre Phil Defer') followed by the short 'Lucky Luke et Pilule', both collected in 1957 in his eighth book from Dupuis.

Here are some of the rare covers I was able to find. First some that were created by André Franquin (click to enlarge):

Here are some of the covers that were created by Morris. They really look like the style he used on his first Lucky Luke comics stories from the mid forties. Very inspired by early Disney animated shorts and other cartoons:

I think this last one was done by Willy Maltaite (Will) who worked with them at the studio of Jijé, but it is unsigned, so I can't be sure: