Kind of hard to do when no travel ban existed at the time - how do you provide evidence that something didn't exist. What DID exist was a travel advisory, 81-331, issued in August of 1981 and which warned that 30 day visas were required to travel to Pakistan and that such visas were available at the airport for tourists only. All others would need to get their visas ahead of time.
So if travel to Pakistan was banned altogether then why would the State Department be issuing warnings about tourist visas? The fact is that there was no travel ban to Pakistan in 1981 or any other time that I'm aware of. So now the ball is in your court. If such a ban existed as you say then where's the documentation?
On any given subject, there seems to be a FReeper who has dug into it far deeper than the general public.
Again, thanks! You have just upheld FR's (and your) reputation...