Here is a suggestion for the Merseyrail Wirral Line: The Merseyrail Wirral Line runs between New Brighton, West Kirkby, Ellesmere Port and Chester with an additional loop of track going through Moorfields, Liverpool Central and Liverpool Lime Street. Map of Line: Map Of Track: The stations on this route are: West Kirkby, Hoylake, Manor Road, Meols, Moreton, Leasowe, Bidston, Wallasey Village, Wallasey Grove Road, New Brighton, Birkenhead North, Birkenhead Park, Conway Park, Hamilton Square, James Street, Moorfields, Liverpool Lime Street, Liverpool Central, Birkenhead Central, Green Lane, Rock Ferry, Bebington, Port Sunlight, Spital, Bromborough Rake, Bromborough, Eastham Rake, Hooton, Little Sutton, Overpool, Ellesmere Port, Capenhurst, Bache and Chester. This route has a total length of 33 miles with 34 stations and the rolling stock is the Class 507 EMU, in a yellow Merseyrail livery.
Some good variety there. Would be nice to incorporate the Stock Interchange line somehow as well....? Or even the Birkenhead docks? (not sure they are in any sort of use any more though??). PS Note the spelling though - West Kirby with one K, compared to the Northern Line's Kirkby with 2 (although both pronounced the same).
Having another think about this (and it may depart from your original point), the track used to continue past West Kirby and down the west side of the Wirral, through Heswall. So apologies if this is not your wish, but a period route set pre-Beeching that used the whole of the Wirral loop line sounds like a nice idea too!