There were no prohibitions for Americans entering Pakistan in 1981. There were State Department travel advisories warning amcits about terrorism and other violence. I know that as a fact having travelled to Pakistan frequently during that period, i.e., 1979 to 1981 as part of my official duties in the State Department relating to working with the Pakistani government on the rebuilding of our embassy and apartments, which were burned down in 1979 when a mob attacked it on the rumor that the US was involved in the takeover of the Kaba in Mecca. There were plenty of private amcits in Pakistan.
Thank you for the clarification, that information I never heard. I do know that I need to learn more and I appreciate you helping me along. :) I thought it was a Marshall law of some sort and it was prohibited.