yup. As someone who works with casting lots of things, I can only imagine how unpleasant it would be to cast -that- in plaster. takes a while for it to firm up enough for a good impression, and plaster *never* comes out of hair– due to a studio mishap, I got nearly-set plaster all over my right arm a few months ago, and it took 4 hours to painfully peel it away from my arm hair, and my arm still has bald spots where the hair was ripped out at the root.
Would have been much better to cast the stars' 'members' in alginate, and then produce the positive by casting plaster in the alginate impression. of course, I don't know what the cost and availability was of alginate in the 1960s and 70s