Thought I'd check the tender to loco coupling as the extra 4mm length at the back was concerning me. Glad I did before going any further. For those who do not know, the current spec Brit chassis connects to the tender via a pin under the cab fixed to the chassis not the pony as in earlier variants.

Here's the result on the widest setting of the drawbar

and this one shows how it all connects

Fine if I don't expect the loco to go round curves!

The plan is to lose the chassis pin and fit a new one to the pony truck that is approx 3.5mm further back than the current item. This should give me the clearance I need for 2nd radius curves and still give me the option of close coupling for display/straight track