Complex sentence: Thompson's first choice for the role of MacKenna was Clint Eastwood, but he was offered the lead role in "Hang' Em High" (1968) and subsequently Gregory Peck replaced him.
Split into simpler sentences: Thompson's first choice for the role of MacKenna was Clint Eastwood. However he was offered the lead role in "Hang' Em High" (1968) and subsequently Gregory Peck replaced him.