How about Cleethorpes - Scunthorpe - Doncaster? If you include Immingham and Grimsby Docks, there's huge potential for freight activities (hence "Freight Capital of the North"

), as well as a huge mix of semaphore and colour-light signalling.
If that's too big (in content, not length. After all, Scunthorpe Steelworks is nearly a route in itself

), I'll second the Nottingham - Skegness suggestion - as mentioned earlier, it does pass under the ECML at Barkston, but most services continue straight ahead at Allington Jn., into Grantham where they reverse. At the moment, they then wait for a path north along the ECML to Barkston South, but soon they should be able to head back to Allington and use a new chord there to access the Skeggy line. And there's a good mix of freight (to Boston), engineers (lots over the next month or so) and charter (including one in April which I'll hopefully be travelling on

) traffic. Plenty of semaphore signalling too!
I'd be willing to help, in any way I can, with either of these two - they're both fairly local to me, and I've spent lots of time on and around both too
