Complex sentence: At this time (around 63) the band was let loose on the public as an R&B group, playing Muddy Walters, Chuck Berry style material, and called themselves the "Stateside Souls".
Split into simpler sentences: At this time (around 63) we let loose on the public as an R&B group. We were playing Muddy Walters, Chuck Berry, type material, and called ourselves the "Stateside Souls".