Sadly it sounds likeI the frame Miguel is looking for is not currently hanging in Neal's basement.
(You sure about that, Neal?
)
No, but seriously, i have, or have had, a few bikes of the kind you're thinking of.
The first was a Raleigh Lenton Grand Prix that i got from Neal. Nice plain gauge 531 frame, similar to the Super Course. I ran it with an FM hub for a while, then reverted to the original 2×4 derailleurs, then moved it on to another forum member. Cool bike!
A recent addition is an Armstrong Moth from about 1950. I got the frame from Neal. I'd say this might be what you want, Miguel, but it's a complete bike, not a project.
Aside from those two, and perhaps something I've forgotten, Neal is in no way implicated in the Norman Rapide, Holdsworth Sirocco, Fothergill, Lambert, Falcon, 1963 Lenton Sports, Drysdale Sport Tourer, Schwinn New World, 1951 Lenton Sports, and other projects.
The perfect bike will fall into your hands sooner or later. But in the mean time I would probably find a placeholder frame and start assembling something around that.
There are a few common English bikes from the early seventies that have frames indistinguishable from the frames you're looking for. Raleigh made the Super Course, and other makers offered something similar-- Lambert, Falcon, Dawes, Holdsworth....