Almost got it, leaving aside the obvious that you've quoted. The front sandboxes are fixed to the chassis and they sit in line with the others along the chassis side where-as they should stick out on a solid bracket so they come to within approximately 2mm of the footplate edge making the front view look bulky under the beam, check a 3/4 view photo and you'll spot it. I've built a few etched 4F chassis and some were right, some the same as Bachmann. Even Airfix had them sticking out a bit but that horrible push along chassis had to be binned. Oh and the guard irons are no-where near wide enough, they don't even come out to the OO wheelsets. Okay, rant over, just annoyed they can't get it right when previous models were, nearly.
The splashers on the Bachmann model are still, of necessity slightly over size but better than the Airfix ones by 1mm and are a nice fit in the metal footplate if a little widely spaced, good for the wider gauges though the measurement inside at 22.2mm doesn't leave much clearance for P4.
Personally I'm in a quandary whether to re-chassis or save time and just re-wheel, rectify and pack out the chassis to EM. I have some trial etches for a 4F chassis so I may mod one for this Bachmann model, afterall it's basically a good model and with a bit of work a great model but then so can the Airfix one be. Talking of which, the two side by side show a difference of just over a mill in the length of the firebox but the detail is much better on the new Bachmann model. All other dimensions are very close and the chimney shapes are similar but as someone else has said - are they correct.?
One last thing, talking of the front sandboxes, how does one fill them when there's no filler cap on the footplate. Oh dear.
I think it's a good model and it runs beautifully out of the box, add some detail, change the buffers for your period if you need to. And, just be grateful there's no gearbox under the boiler to offend the eye.
Dave.
And I'm not going to be drawn into a debate on chassis Vs frames, totally different things, so there.