Although the premise relied a bit too much on the unlikely coincidence that the spy's "double" should pop up to be mistaken for him just as he was about to be killed by an East German agent, we'll forgive the creators that bit of wild invention, as it made for an entertaining setting for the rest of the series.
The series had three problems:
First, it was a half-hour show in a genre that cried out for an hour-long format to fully develop the plot for each episode.
Second, It was put on the schedule opposite "Green Acres" at the height of that sitcom's popularity. "Green Acres" was a spectacular #6 in the Nielsen Ratings that season.
Third, it had no real lead in. It followed "The Monroes", another debut series with no following, which also lasted only the 66-67 TV season. "Green Acres", by comparison, had "The Beverly Hillbillies" as its lead in.
So "The Man Who Never Was" was doomed before they ran the first tape.
It appears that the only way to sample this fine show is via two composite movies where are currently available on Youtube.
"Danger Has Two Faces" includes parts of episodes 1, 2, 3, and 5. "The Spy with the Perfect Cover" includes parts of five later episodes.
Watch "Danger" first. Although the quality is terrible, it's still worth a look.