Year – 1954?
Basically when Vespas were the coolest, most glamorous thing. I’m imagining this came out after the Audrey Hepburn movie Roman Holiday (because she rides a scooter in it) and not after the notorious Mods on Scooters versus Rockers punch up on the beach in Brighton (1964). So Roman Holiday was 1953. Also the pattern gives the amount of yarn in how many ounces you needed rather than how many balls, which is a change that had definitely happened by 1970.
Size – 34, 36, 38 inch busts
Yarn Size – DK? I’ve searched for Apollo Triple Twist and can’t identify it.
Looking at the tension and needle sizes given in the pattern (old UK sizes 3 & 5 = 6.5 mm & 5.5 mm) the yarn appears to be chunky weight. It’s definitely quite a lot thicker than DK.