I am new here but I thought I would give this friendly forum a go for identifying a frame. I got it from the original owner and it was supposedly competed on in 1968 and then unfortunately made into a commuter bike with mudguards. It was therefore drilled in several places. However, it is a nice frame and the other frame I got from this owner was a late sixties Pogliaghi frame so I do have some hopes for this one although not expecting anything like the Pog.
So the details and numbers…
Bottom bracket threading is British. Nervex lugs. Campagnolo dropouts. Double plated fork crown. A noticeable feature is the diamond on the seat stay caps.
The serial number which is stamped on the side of the seat lug in very small numbers read 73930 or maybe 73 º30
There is a “2” stamped on the steerer. Seat post size is 27 mm.
Ok what did I forget?
Not that much to go on but with so much expertise here I thought it worth a shot. Many thanks for reading.

Hi, welcome to the forums!

Due to the diamond I thought it was definately Italian, cause they hve a thing with cardgames. But with British threading? I am no expert on trackbikes but I believe someone here is going to help you out.

Btw holes drilled in dropouts and rearstaybridge but not the fork? Lucky!

very interesting: no doubt the lugs are Nervex, but the rear sockets on the headlugs, and the entire seatlug, is not the usual Nervex pro pattern.
I think that's the angle of the seatlug, something Nervex did...and the BB shell is very different, it might be a Nervex, too but not like any I've seen. The whole thing has a "British" look to it, however, a 27.0 seatpost points to either plain gauge 531 seat tube, or...track-specific tubing (??) or Columbus SP or Aelle...I doubt the last 2. No idea as to that stay cap, very much unique!
Did you check the steerer for "rifling"?

Thanks. I was not aware of the rifling in the columbus steerers. No rifling though so probably Reynolds 531. As to the stay cap the previous owner had another frame just like this one (as far as I could tell) except it was a size smaller and lacked the diamonds in the stay cap? He has no recollection to what these frames were. He did say that he at some point rode a Danish road bike.

Also forgot to mention that there are no cut outs in the bottom bracket shell.

On the other hand I find no rifling in the steerer of the ca 1968 Pogliaghi track which should be Columbus tubing. right? Was there no rifling at this time?

Think I might have seen a seatstay cap with a diamond on it, a Schroeder/Schroder? Its a Dutch bike or maybe Danish.

Could it be a custom-built "one off"?

The "rifling" was probably in the Columbus steering tubes about that time, (but may have come into use just a bit later) however, that's one place where many builders used whatever they had on hand. Many Columbus-tubed frames had Falck stays and forkblades, as well as Falck steerers.
IIRC Pogliaghi was also one builder known to have mixed frame tubing (brands and gauges) to get the "secret sauce" he wanted.

As for the Schroder/Schroeder idea: there may be something there. I did a search and found one image of a very old example that has nervex lugs that also feature unusual rear sockets (unusual yes, but still don't match the OP's). The Danish spelling is with an O with a slash, it seems to Google better if you spell it with just the plain "o", not "oe". No pic of the staycaps, but other Schroders pix don't show this "diamond" feature.

They (Schroder) are still in business but now located outside of Copenhagen in Hellerup. You could ask them, but it would come down to whether there's any "historian" on staff...they are rep'ed in Colorado by adventurecycle.net, so you could ask there, too.

Apparently this brand was also fairly popular in SoCal as one of the early retail pioneers ("Pops") sold them out of his shop (in Manhattan Beach?), maybe an LA member remembers.

Couple details about the pic: it's a track bike, it's all 531 tubing (says the label) but the forkcrown is also different to the OP's. The head decal shows the name as P. Schroder (for Peter Schroder), later decals just have Schroder and a red "S" in the middle of the "wreath". The company was sold in 1960, maybe marking the change in name.

I could definitely buy the Schroder hypothesis. Big thanks for the idea and the research. I will send them an email with a picture and see what comes out of it. Will let you know if I get an answer... Meanwhile I will be searching for diamonds and trying to figure something out about the Schroder serial numbers.
I actually have had a small worn down mid to late 70s Schroder. No Nervex lugs. I liked the red and white color scheme and the decals. Hand made in Copenhagen they said.