my take on guided missiles,

They would more than likely be a thing but do keep in mind, IRL the first American designed Aim-4 falcon guided missile was designed in 1949 and began use by 1956 (and in my opinion, probably among if not the best AA missile at its time) It was still highly ineffective. Even more so, IRL by Vietnam, missile technology wasn't that great.. 

Inkdrop does bring up a point though regarding old missile technology. 

Personally, I'd just have them as an equivalent to missiles of that time. IT's what I'm doing.