Complex sentence: He trained with Vince Gironda, another well-known bodybuilder of the time, and became best known for his arm development, particularly his impressive and unusually long biceps, which allowed for good development and shape.
Split into simpler sentences: He trained with Vince Gironda, another well-known bodybuilder of the time. Scott is best known for his arm development-and perhaps most for his impressive biceps which were unusually long, allowing for good development and shape.