Cheers all for the comments and input. Gareth, yes was the wife as it needed someone to hold the "test rig" AKA batteries and tape etc... no cunning plans per se.... but they are often on my mind
As for the chimney I had a look and as it is supposed to be narrowish gauge I think it's OK for now. It's an easy fix. I think I will now just paint it black, with red wheels and then, leave it for a while and decide what final changes might be good. I will also fit the gubbins for battery RC, before final details and paint are added.
Interesting comment on the bolier diameter. I went to great lengths to make my own boiler and firebox as I had read that they should be big diameter and shortish- a benefit of the Garratt config not having wheels under it for good steaming. However whilst i can change details I am am not going to rebuild it regardless of it being right and wrong- had enough of glue, cutting myself for this year
bye for now.