This I believe to be a Peugeot P-something, metric tubing, Simplex dropouts, 26.4 post.
The headlugs have that reinforcing ring, but there are four flats, two each top and bottom, parallel with and square to the head tube (pic is distorted):



They're nice flats, all the same size and they don't look hand-done, but the only reason I can think of is to have a go at twisting the frame.
A worrying prospect...

"A worrying prospect..." oneclick

And a step in the process that goes on in pretty much every bike factory when making a frame. IMO the question isn't "did they" but "How much was needed", which we'll never know.

The first thing I thought of is opposing small flats did serve to aid the aligning process, or maybe the measuring aspects. When I am measuring main frame twist I want to have the contact points (of the feeler or dial indicator tip) as far apart (upper to lower) as possible to increase any deviation amounts WRT the seat tube. But the surface right around a lug's shoreline can be "lumpy" of sorts. Brazing filler residue, too aggressive filing and that heat distortion thing all combine to make the surface not so "flat" after all and the lugs might have not been filed equally thin. To help increase the measuring contact points far apart and rely on the head tube's ID (where the fork is) I have a shaft that goes through the HT and had same diameter end cones loaded against the lug faces.

I can see a person filing down the two flats so they have the same thickness, relative to the reamed ID. Then when aligning the feeler pointer contact is in the same place, the same distance from the HT axis and is as far from the other end as possible. Seems like a lot of work to avoid having a tool that might need to be used with pretty much every frame the factory makes.

So here's a story. (Yes, I am full of them. And I make little claim of being correct). I worked for Geo. Rennie Bicycle Shop for about 7 years back in the later 1970s/early 1980s. A pair of childhood friends started the shop on one's back porch and after a couple of decades grew to be the service and "pro" (as racing sort of existed back in the 1960s/1970s) shop in our area. We sold Raleigh, Peugeot and Motobroken as our main lines when I started. Remember this was just after the first gas shortage I was an adult during. The shop sold a zillion bikes (some funny stories about this but not the one I am taking too much time writing right now) and both Raleigh and Peugeot had invited select US dealers to their factories for tours and hand shakings. Again, there are stories about the Raleigh factory (involving TDC freewheels and 531 decals) but it was the Peugeot factory tour that Jack (George's partner) told me about that pertains here. At the end of the frame brazing "line" there was a pile of raw, just brazed, frames and a guy would pick one up and (with respect to the Taylor Brothers across the channel) sight down its length. As needed he would pick up a huge leather covered mallet/hammer and whack the frame this way or that way, as needed and confirmed by his very experienced eye. No lasers, surface plates, dial indicators, feeler gages.

I don't remember if Jack or George ever got to tour the Motobroken factory(s). We dealt with more Peugeots than them and Raleigh was 2/3 our total sales so we didn't see many high end Motos. Too bad because I felt my Super Corsa was one of the sweetist handling road/race bikes I have ridden. Andy

I have a feeling those flats might have been done by a shade-tree mechanic in order to help knock the headset cups out with a big punch or (more likely) a big screwdriver ?

vintage cellar- Good suggestion and one I should have thought of first. here's a shot of a unicrown fork I made a few years ago with a similar crown race removing scallop. There's one on the other side too. Andy.

Reminds me of this 1960-ish Bianchi that Bob Freitas was in the process of restoring.



The lugs were extensively thinned, beyond what a normal Specialissima got, and it was chromed (chrome removed for restoration, too rusty) so Bob was pretty sure this was done at the Bianchi race department, i.e. orignal not aftermarket. So, must have been a "special", for a top pro racer, or the CEO's wife or some such.

Also the deraileur hanger had been removed, so it's fun to think this could be one of 'Le Bici Di Coppi'. Unlikely, but Coppi did have his track Bianchis made with road dropouts, gear hanger removed. More likely made for a "Coppi cat" (see what I did there?), someone who wanted his track bike to look like Coppi's. The bikes Coppi actually rode are probably all accounted for.

I've worked on a few Specialissima headsets and they did not have those filed scallops for removing the headset cones. (I almost wrote "cups" out of habit, but those headsets had the cones pressed in the head tube. The crown race was a cup.) I was always able to knock the cones out, but it's definitely not easy, just a thin ledge exposed for hitting with a punch. The punch needs a sharp edge, any bluntness and it'll just skip past the ledge without budging the cone. But I digress!

Anyway back to oneclick 's Nervex question, I kinda doubt it's for headset removal, or I hope it's not. Headsets are so much easier to remove by hitting them from inside the headtube. And you'd probably have to file the flats with the headset installed, probably knicking the chrome on the cup or cone in the process. Who would do that? Even if you were throwing away the headset as soon as it's out, that's still more work than just hitting it with the same screwdriver, but from inside the HT.

Ugh, maybe just because your screwdriver isn't long enough? Is anyone that lame a mechanic? (Rhetorical, yeah I know there are.) Sad story if true.

Getting way off topic (C&V question not framebuilders), but I'm curious, what Super Corsa do you mean? The syntax makes it sound like that's a Motobecane model, but I've not heard of one, and I worked for a major Moto dealer during those years. Sounds like you're talking about a Gitane, or Cinelli? But I know Moto had different model names in Europe than in the US, so maybe it's a Euro-only model.

Mark- My mistake it was a Gitane Super Corsa, not a Motobroken. Still it was a really nice handling bike, whatever the brand Thanks for the memory check. Andy