So I was wondering whether you could shift it in your original modelling programme ?
Er, not sure how to do this Jon.

I've been centreing the axis of each part to the Object. Each Object is a child of the footplate (main) and then the main is centred to origin - position 0,0,0. This puts the loco or tender on the rails OK, but how you shift fore and aft I just don't know. And do you move the loco or tender or both? I guess I could move the main axis but goodness knows what this would do to all the parts! New as I am to modelling, I'm a bit reluctant to try something so drastic............Strange, I never had this problem with the MN which seemed to have the corrrect gap from the start.
Are there any modellers that can advise? I know Mickrick had similar problems recently, and there wasn't an easy solution.