At the time of the sale PA flew from LHR to Miami, Washington, New York, Detoit, Seattle, San Francisco, Los Angeles, Frankfurt, Hamburg, Amsterdam and Oslo. There were many other rights not used (eg. Paris, Brussels, Delhi). I think UA actually took over the routes in March 1991?
UA didnot purchase the Miami and Detroit routes which PA transfered to LGW. These went to DL when they bought the remainder of PA's transatlantic routes in November 1991. Miami was shut and Detroit sold to Northwest who continue to operate it today.
I'm currently creating an Online (Original) Pan Am Timetable of September 1990. So far flights cities Albany through Belgrade are complete with Berlin half online. Please view it at www.atmosphere.be/travel/jjd
simply click on the "Pan American History Link" link to view it. It's a long term project but any support is very welcome
Pan Am was the first airline to fly "in" to LHR longhaul, a flight by a Connie from LGA the day after LHR opened. An Imperial (think it was still Imperial then) aircraft took off for New York the day before I believe.
Hope that helps!