Was a 7300-mile non-stop flight possible in 1979?
Even for zero payload, no B707 model is able to fly more than 6000nmi (11111km). B727 even has less range.

However, Iranair planned to run Tehran-LAX flight, which length is 12222km, but never materialized because of 1979 revolution. The flight could have been operated by the 747SP (introduced in 1976), similar to their Tehran-JFK route.