Pete,
only just picked up on this topic, that Mason Bogie looks very much like the one built by my friend Peter Janes round about 2000.
Peter was a prolific ‘maker’ of loco’s, always trying to make something ‘different’ from stock models. As you say this one was made from an LGB Mogul, Peter didn’t want to cut down the length of the original boiler or tender to make it more prototypical, it was very much a characature using what was already there, I think it worked out OK. Sadly Peter passed away in 2005.
The model was passed on to Garden Railway Specialists in exchange for more models for bashing shortly after it was finished and I caught up with it some years later when owned by Dave Buckingham. Dave passed away about ten years ago and I think it may well have gone back to GRS for resale at that time and I don’t know the history since.
Your right about the electrical set up, either track or battery power by changing the plugs, Pete was a firm believer in simple electrics and the Chimp was probably one of his first dabbles with electronics which he never really got to grips with!
I’m pleased to see the loco again after all these years and I’m sure you will get enjoyment from owning a unique model, hopefully the bit of history I have been able to give is of interest to you.