Complex sentence: Langshaw lived in London in the 1750s and Lancashire Museums suggest that he knew Handel, although other sources suggest that his reproductions of Handel's music began after the composer's death in 1759.
Split into simpler sentences: Langshaw lived in London in the years either side of Handel's death in 1759 and Lancashire Museums suggest that he knew Handel. Other sources suggest that his reproductions of Handel's music began after the composer's death in 1759.