Oh no, you're doing fine. I enjoyed reading the page above.

I believe you're onto something with the Sport model as this freewheel will definitely need a larger lock ring.

Update: I just reread the Yellow Jersey site again and this is what's said about the Sport...

"These hub axles interchange perfectly to Helicomatic Sport hubs. The models Helicomatic 500 and Helicomatic 600 use a different and not available cone . Top quality highly polished 700 Professionnel Helicomatic hubs use both an unusual cone and a uniquely fine threaded axle . Neither part is available. 700Pros use a larger chromed locknut in that special thread, also not available. Type 500, 600 and 700 Professionnel use smaller ball bearings. If you open your rear hub and see nine bearings which are 1/4", then you have a Sport hub and this is the correct axle set. If not, we have no parts here for you."

Seems like the difference between those various models is in axle and cone sizes, not hub outer diameters.

I guess you can take this part about the 700 Professionnel to mean two different things: the "larger chromed locknut in that special thread" refers to "a uniquely fine threaded axle ". Or you could take it to mean it's the lock ring on the hub for a larger freewheel. I dunno...