SD, I have a friend who flies for Southwest. A few years back, he restored and flew a T-34B for a while. I think he later sold it. He once told me he had to be careful how much recreational time he flew, since his log book entries compared to his log book entries for the 737 he flew for pay could not exceed X hours without a waiver, or he'd violate a rule (IIRC, an FAA rule). Not sure enough about the rules to say more.