Complex sentence: He then switched to playing custom Fender Stratocaster guitars that were modified with humbucker pickups, whilst also endorsing DiMarzio pickups; during this time he was pictured in a contemporary DiMarzio catalogue (around 1981) playing one of his modified Stratocasters.
Split into simpler sentences: He then switched to playing custom Fender Stratocaster guitars that were modified with humbucker pickups. Holdsworth also endorsed DiMarzio pickups during this time; he was pictured in a contemporary DiMarzio catalogue (circa 1981) playing one of his modified Stratocasters.