There's a flood of these mid-century instructional videos appearing the Web just over the past couple of years, right up to the present week. (I quite like the Jeff Quitney account on YT https://www.youtube.com/channel/UCM-kjdrQge9AACfB3MSRyrg , a fairly nice firehose of videos in good quality, which even seems to have some that aren't on the IA.) One thing I've taken from watching them is that US accents seem to have changed a lot in the past few decades: you hear presenters with accents that afaict don't seem to exist anymore. Jam Handy's is one, but there are more dramatic examples.