The McGee song you are after may be 'When the Wagon Was New'. If so, Sam variously said that he 'got it from a vistor from Illinois in the 1930s' or that he (Sam) had written it in the 1920s. You will find information in this thread:

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Clarence 'Tom' Ashley recorded 'Walking Boss' in 1961 for Eugene Earle and Ralph Rinzler. [cf Smithsonian/Folkways SF CD 40029/30]. Ashley told Rinzler that he had learned this track lining song while 'busting' outside of pay shacks in West Virginia coalfields. Rinzler noted that 'Newman Ivy White and Odum and Johnson include identical texts for this African-American worksong. White's text was collected in Alabama in 1906. 'Walking Boss' appears in Herbert Halpert's handwritten field notes from his 1939 collecting trip'. See also this thread:

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'Whoa Mule Whoa' was recorded prolifically by old-time artists in the 1920s - Uncle Dave, Skillet Lickers etc. Evidently, it was reported as early as 1911 in the 'Journal of American Folklore'. There is a thread in the forum:

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The lyrics to Gun Cannon's 'Whoa Mule, Get Up in the Alley' may be found in this thread:

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Hope the above is of some help,

--Stewie.