A long time ago I converted ye olde Hornby Black 5s using Crownline kits into the 2 Caprotti variations and also Coronations into 46256/7. Also, somebody did a Stephenson Valve Gear set for 44767 which I never did buy.
Crownline 'retired' many moons ago and I wonder if anybody is providing parts to do similar conversions to the current Hornby models?
All I've managed so far is to fit a double chimney (44766) and build a self weighing tender.