Complex sentence: Del Dettmar left prior to the release of "Hall of the Mountain Grill" to live in Canada, Alan Powell joined as an additional drummer, and science fiction author and friend of the group, Michael Moorcock, stepped in to read poetry at their concerts.
Split into simpler sentences: Del Dettmar left prior to the release of "Hall of the Mountain Grill" to live in Canada, and Alan Powell joined as an additional drummer. Science fiction author and friend of the group, Michael Moorcock, stepped in to read poetry at their concerts.