I had that same problem and was given a starter handle without a pin. Just need to fabricate a pin. However, yours should be a standard special engine and that may translate to early Triumph. I saw an early Triumph handle for sale but passed on it. You might try looking for one of those.
Or worse case, you might just have to find a working S1 handle to get the specs, and fabricate from something else.
Cheers,
Mark
