So a bit more on M15 (LNER F4) options
Here's two from my rescue collection awaiting Thier turn.
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The one in front is pure Gibson etched brass with a Stephen Poole white metal body on the prototype 52F chassis. Both body options are a good starting point for a model and it really depends on your medium of choice.
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The issue is with the chassis. The loco has a very long fixed wheelbase (think that's bad try and F3) and the problem is the Gibson and the Rummney are both unprototypically lacking the radial trucks that these locos had.
On the left is the sprung Gibson F4 chassis in OO which won't take anything less than a 4ft radius curve whereas the EM gauge 52F offering on the right has prototypical radial trucks and also a joggled frame fire and aft meaning it will glide round a 2'6" curve without issue
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Not something Nigel needs to worry about on the graceful curves of Elmham market but in much tighter environments like the awkward space I have it's a real bonus.
Also a plus is when you have the body shell on the joggle is completely hidden by the loco steps