Diverge in 1939. The germans aplogise profusely and go home. Ignoring environmental stuff. Southern Bullied pacifics, Q1s, N/U/S15-generation still going (just), Adams Radials and Beattie well-tanks and terriers survive. What would fill the Leader niche? LNER Monster 4-8-4/2-10-2s on big freights and slow passenger trains. A4s coming to end of life as fast passenger engines. O4s replaced by O1s? LMS Black 5s and 8Fs for everything that the Duchesses and 4-8-4s don't do. Diesel shunters in the yard GWR Counties, Cathederals, 28xx, modified Halls and modifed manors for everything else?