Hunts cross west junction in the 50s could be good, I'm not sure what kind of space you've got to work with but it's got a concrete works just behind the track. It's where the Allerton TMD is now.
If you fancy moving to N gauge I've got a 502 slowly in development I've been collecting pics and info about the northern line for a while, so when you figure out what it is you're doing I might have some reference that'll help.