Notice the big baskets and the slow return of the poles. The new poles return much faster enabling a much higher tempo for skiing. The highest speed is in a V2 Alternate. Apparently the V2 was still to evolve. Amazing. These old videos are very informative for young skiers.
A great deal of the increase in speed of modern XC skiers is due to fluoro waxes (in the process of being banned, thank goodness) improvements in boots, skis and poles. I wonder how fast modern skiers would be if they had to do a race in this vintage equipment, with old non-fluoro waxes!!!