Conversation so far:
What does Mark Donohue have to do with the ford GT40?
Ford signed Mark Donohue to drive one of their GT-40 Mk II race cars campaigned at the 24 Hours of Le Mans by the Holman & Moody racing team.
when did Mark Donohue Join Penske?
In 1967, Penske contacted Mark Donohue about driving Penske's brand new Lola T70 spyder in the United States Road Racing Championship.

Question: Was there a reason he decided to join Penske?
Self-contained rewrite: Was there a reason Mark Donohue decided to join Penske?