Good time to share a secret Frenchie tip, one of the best I can about retrofriction and the simple "sun" Simplex levers:

Here's the best $10 you ever spend: https://www.amazon.com/dp/B00L8NDVD6/

I know it's "Schwinn" branded but the shift cables fit perfectly and the cable kit overall is good quality. I bought a bunch of these kits when they were on sale a few years back for $6.99/ea just to use on cheap flips, never thinking to try it anywhere else. I'd previously been filing down my barrel heads on a pile of NOS Huret cables for my bikes before because I had them and... I mean, let's put French on French, man...

Well, I was on a budget-build for a co-worker short on cash a while back ('82 P10S I got for $40) and I wasn't about to put $20 in Huret shift cables on his bike, I was already doing him a huge favor with a charity rebuild. Cracked open that Schwinn kit and was absolutely shocked when they slipped right into the sun-branded levers that are too damn tight for most other cables, just like the retrofrictions are.

Kid has since put thousands of miles on the bike I rebuilt for him and they're still shifting as clean the day I put them on and tuned it out. Bonus, you get a full brake housing+cable set with both end types that fit Weinmann/CLB/etc. like a champ.

Updated to add pic of kit: