Noticed this pair parked at work. The 747-400 is N661US and is the very first -400 produced. It was retired yesterday and will become part of the Delta Heritage Museum here in Atlanta. It was produced in 1988 and served as the Boeing test bed before being delivered to Northwest Airlines. I don't have the details on the MD-88, except that it is clearly much smaller than the 747. The 747 is configured to carry 424 passengers. The -88 is configured for 160 passengers.