Robert99 and 377, thank you for your feedback.
I am a ME and while as a pilot understand how to use avionics, I am not that skilled in their design. DME was used by the 727, as they report their position via a DME distance in the transcripts. When I first started flying in the early '70's, a local pilot had DME in his single engine plane. It was quite the talking point, as it was expensive and not many small planes had it at the time.
But as I state, make no mistake, Cooper had something to tell him where to jump. If he jumped out at Pigeon Springs, I would agree that he jumped blindly, but if you look at the FBI Landing Zone Map, Cooper used the winds aloft data and his drift time to pre-calculate his jump point, so that he drifted towards Merwin Dam and the open fields south and west of the dam. This is not a blind-luck jump. Even Ted Mayfield said the man knew what he was doing.
And it's true, hand held NAV/COM's have been available for almost 30 years. How do they differ from the devices of 1971? Surely they are smaller, but is there any other basic difference? How come cell phones work on a plane at the gate or during taxi? You are still in a metal plane?
I will leave it to you gentlemen to decide how Cooper knew his position, but you will need to be creative and ingenious like Dan Cooper. As I stated in a previous post, Cooper knows he can't jump on a clear night, as it is a sure recipe for capture. He has planned for a jump that evades visual contact by the chase planes. Now tell me how he precisely determines his jump point. You've got a month or two to devise a system and do trial runs between PDX and SEA.