I have an older Serotta ('87 Nova Special X) set up with 8-speed Chorus ergo levers, and I have C Record threaded hubs. I'm using a 7-speed Dura Ace freewheel, and the shifting is spot on perfect. My rear derailleur is an 8-speed Chorus. I have another set of wheels with a Dura Ace 7-speed freehub, and that rear wheel works great as well. I've used both a KMC 8-speed chain and a Dura Ace 7701 9-speed chain with equally good results. It works because the spacing for Shimano 7 speed is the same as Campy 8 speed.
Another option would be to try to find an 8-speed freewheel, but after researching and reading up on them I decided not to.
I am using a threaded C record hub on my vintage TT bike. I thought that the hub is 126mm, and I can always go check.
When campy etc went 8-speed then spacing changed to 130.
Anyway the sprocket spacing is the same from 7 to 8 speed, meaning that an 8 speed shifter will shift fine on a 7 speed cluster. I'm using a 9-spd chain BTW and the shifting is perfect - nicer than today's.
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