Complex sentence: Spearheading the fundraising campaign will be a world record attempt by the Director of Music and organist at St Giles', Ashley Valentine, who will be attempting to set the world record for the "longest marathon church organ playing" in June 2015.
Split into simpler sentences: Spearheading the fundraising campaign will be a world record attempt by the Director of Music and organist at St. Giles', Ashley Valentine. Ashley will be attempting to set the world record for longest marathon church organ playing in June 2015.