You are right about the spanish tuning, but Muddy was tuned down to what sounds like an open F# if you listen closely. That recording was made in 1941 actually when Alan Lomax from the Library of Congress came to Mississippi before he was to go to war searching for Robert Johnson. Alan ran into Son House and who told him that Robert was dead, so he was recorded instead. At the end of the day, Alan asked if there was anybody else he should meet to record from around the area. Son recomended a young 28-year-old who was at the time going by the name "Muddy Water" (before the S was added). Muddy was recorded the next day and started with 'Country Blues', his variation on 'Walkin' Blues'. There were plenty of interviews that are cool to listen to as well. Alan came back the next year to record Muddy and by the end Muddy had made $20! By 1946, Muddy was in Chicago. He did later record Walkin' Blues in Spanish tuning but tuned up to A with Big Crawford on bass and Muddy was on electric guitar. Band members were only added from there.
