The king of route merges is known as Danny on Steam Workshop, I’m sure someone here will know how to reach out to him. There may also be You Tube videos on the subject.
As for Crouch Valley, I can’t play it because I know the GEML too well. The Shenfield to Liverpool Street is wrong in so many ways, gradients all over the place, buildings randomly placed and very repetitive. However the Southend Vic end is really good so if it is at all possible to update the branch and add it to the DTG route I’d be delighted as would many more.
One other thing, one of the route builders and I wish I could remember who has a GEML extension next on the list, the Clacton and Walton one. If the Gainsborough line got added too we’d have a complete Great Eastern area freeware upgrade. It might be worth reaching out to see if anyone wants in on the project, we’re a helpful bunch.