vonfilm 

...that a Superbe Pro RD will cooperate with the 13/28 6 speed Helicomatic freewheel and a Campagnolo Xenon 50/34 compact crankset and the stock Simplex FD on my 83 Peugeot PFN10? Velobase says that Suntour called for a 26 tooth maximum cog and 26 teeth of chainwrap. Isn't that too conservative?

JohnDThompson 

Since the Superbe Pro was a racing derailleur, I doubt that it would have a long enough cage to wrap the chain on the gearing you suggest. Perhaps a long-cage Cyclone would be a better choice?

repechage

I agree. But, if you don't need the stupid combinations of 34x13 or 50x28 then you might get by, that is might. I think that still puts you officially beyond the Superbe Pro capacity. The problem is the 16 tooth difference up front, that is a lot of chain for the short arm of the jockey cage to take-up.

vonfilm 

How well will the Simplex FD handle the 50/34 compact double?

JohnDThompson 

It works fine with a 48/30 double on one of my bikes.

dddd

I've used a Superbe Pro rear derailer with a re-spaced Shimano 12-28t cassette, and had no issues with the Accushift shifting.

As long as you avoid using the smallest few cogs with the small chainring, I see no problem with using a compact crankset.

The Helicomatic 6-speed freewheel is narrow-spaced as I recall, like a 7-speed freewheel.
Their shifting characteristics are somewhat grim, but you could try using a 9-speed chain, that's what I would probably try first.

I would not use indexing with any Helicomatic freewheel.

vonfilm 

My plan is to use the stock friction Simplex DT shifters. I am trying to use parts that I have on hand.