[Arran]

 In my case I would used either 18 or 20 gauge vinyl covered, mostly because 18 or 20 is what I can buy by the 100' roll in a large assortment of colours locally. Most 1940s radios, these things include, are not historically or monetarily valuable enough to become anal over what style of wire to use, just use the best wire you can get for the lowest price.
Regards
Arran