dddd

The OP's bike from 1968 has a Huret derailer hanger on the forged dropout. And the year 1968 might also be the first year out for the Twin-Stick levers.

So I would emphasize making friends with this style of levers. They feature offset (towards the front) pivots, giving added knee clearance while retaining the fine-shifting longer levers.

I didn't know that a Suntour rear derailer would need the Twin-Stick's full cable pull to go across a five speed freewheel. Though with my Allvit and standard-spaced six-speed freewheel I do use up the full amount of lever travel (even with the cable tensioned pretty snug). Never a problem though, I've ridden thousands of miles without needing any cable re-adjustment, and I actually like that the lever hits a hard stop as I am shifting onto the largest cog.

The later-model Supersports (from at least 1971 on) would come with a longer-cage Allvit rear derailer to clear a very big (32 or 34t) freewheel. These also unfortunately featured a different style of claw hanger which positioned the derailer body almost rearward of vertical. Shifting on smaller freewheels improves a lot with a switch to the short-cage style claw (or complete derailer), and I'm remembering now that I put a short-cage Allvit on my 1971 model for the better shifting it offered with my smaller 26t freewheel.