Thanks to Dave Holt for pointing out a glaring error that resulted in a massive gap between the rear driver and the firebox/ashpan. Turns out that I made a last minute change to the frame drawing when I compared the tracing with that of a Comet Britannia chassis. This threw the whole chassis forwards by approx 2mm (6" in the real world), but meant that the cylinders were at least in the correct place on the chassis.
So last night I unsoldered the rear mounting from the frames and repositioned it 2mm further forward resulting in a much better looking gap
Of course this left a gap at the front which I filled with some plasticard packing
However, Dave is right. According to Cox's excellent "British Railways Standard Steam Locomotives" (Ian Allen, first published in 1966 and would sell well if reprinted ) the 2-8-2 as designed was 6" shorter than a Britannia (2-8-2 in red below)
So, do I chop the body to lose 2mm? it looks like the smokebox is longer on the Brit as the boiler specifications are identical. cutting a section out immediately ahead of the smokebox/boiler join would pull the chimney back above the cylinders.
If I don't do it my concern is that there will be a gap between the cylinders and the front fall plate and it might look odd with the chimney forward of the cylinders.
I plan to cut the footplate to take cast lubricators, so some making good will be needed on the top surface of the footplate in any case. The razor saw becons .......