If you want a triple, you could triplize this crank (assuming it's a 144 bcd which I think it is) or you could find a stronglight 93 and triplize it).
https://www.redclovercomponents.com/...riplizers.html
I have a similar choice to make on a Mercier 300 I am rebuilding. I haven't decided yet on the gearing but I'm leaning towards running a stronglight 99 as a double with 48-34 rings and a 14-30 ultra 6 freewheel. New stronglight 99 rings are available from Spa cycles in the UK and they will ship to the US.
I'd be sorely tempted to keep the suntour derailleurs as well even though they're not quite "right" for that bike because they're so good.
Yes this is all Reynolds 531 though I believe the headtube may not be; the forks, main (other than the headtube) and rear triangles are 531.