I can't post pictures as I don't have 10 posts yet. I'm trying to identify a BB on a retro (1980's ?) Rotary bike. The drive side has what looks like a big washer, about 35mm across, with two flats.

The non-drive side has a 24mm nut, and a lockring with 4 equally space notches.

If I can identify it I can get the removal tool, or work out what I need to remove it...

what's a "Rotary" bike ?

post some more so you can upload a pic but from the mental image I get based on words written, I think maybe French, possible
"Lightrace" or Nervar. Here's something from Velobase, look familiar to you?

That looks like it. I’ll post pictures as soon as I can.

The crank axle itself is a square taper, but those other bits look similar.

Her's a pic of a Nervar, this might be for a "Star" crankset but they made other models that used similar BB units. And by "Rotary" did you mean

maybe "Rotrax" ( a vernerable British make)?

Looks promising. So a lock ring spanner, and a Park Tool HCW-4 or similar seems like it'll do the trick

Your first post you state the fixed cup is 35mm, the Park Tool HCW-4 is 36mm so will not work. Also, the pins are useless for your bottom bracket.

I use a 12" adjustable wrench for my BB's that have 35mm fixed cups. My Diamond Tool wrench opens to exactly 35mm

For the lockring, this is a little more expensive than a Park Spanner but is much more versatile and easier to use.

https://www.mcmaster.com/5471a12