The nice thing about using an early 70s SuperCourse for such a conversion is that they don't have a derailleur hanger and are spaced at 120mm in the rear triangle, so a 3-speed hub with a 6 1/4" axle will fit without serious modification. Running cable stops and pulley wheels can be a bit fiddly, but quite do-able. Last weekend I had my '73 SuperCourse equipped with a 5-speed rear hub out for a 30 miler.
