One of the most interesting obscure figures of '60s soul, J.J. Jackson scored a mammoth R&B hit in 1966 with one of the most infectious dance smashes of the decade, "But It's Alright." The New Yorker had worked as an arranger for Jack McDuff and Jimmy Witherspoon before his manager arranged for Jackson to come to England in 1966. Though "But It's Alright," with its classic stuttering guitar riff and sharp horn charts, sounded as authentic as any Stax/Volt single, it was actually recorded in the U.K. with British session musicians. Jackson -- a mammoth, nearly 300-pound man who...