Well, 62 is when Raleigh completely revamped their fast bike lineup with DRs only offered. The GS got the Campy GS but the Blue Streak received the Cyclo Benelux DRs. Huerta could be an option but I am unclear which model would be period appropriate. If you cruise through Disraeli Gears you could find out.

I have a 62 GS with the copper colour, white headtube and Campy GS mechs. Love to see this paint scheme and frame of yours.

bTW, with the proper toothed cog in back, a 3 or 4 speed would handle those hills possibly.