Lively Polly at Wellington Dock on the Overhead Railway. The bridge behind was the L&Y Rly High Level Coaling Railway to Wellington and Bramley Moore Docks.
Amateur film of the LOR from the NW Film Archive: https://player.bfi.org.uk/free/film/watch-liverpool-overhead-railway-1893-1956-1956-online?fbclid=IwAR0oXF3dJZ0duR1nSFFF4hVqVf13NHzEq8eo9t1qSMfGqpkEQa5ypJKGnHI
The LOR employed a Ruston for engineering work trains, replacing Lively Polly. Information on colour/livery seems non-existent? So perhaps something like this image is a reasonable guess? Copyright Idle Drifter, photographer unknown.