That was an excellent film about the building of the northern section of the M74.
Interesting to note that they had at that time ('64-'66 for this film) already planned for the M73 even though it was only completed in 2011.
Also some other good stuff in the (my) sidebar:
https://www.youtube.com/watch?v=G8iLRrt_4Jw
https://www.youtube.com/watch?v=-viFpByHFHU