Yes, and here's a drawing of it. It is indeed an 8F 3C boiler, valves, cylinders and front truck, with enlarged tanks and bunker similar to the 2-6-4T.
I want one. Plenty of numbers left over in the 7000 region... drawing suggests almost exactly the same hauling power as the 8F.
I can also see why they didn't fly - that's a long old tail to wag, both side-to-side and up and down.
Onto further fantasy, with the drivers only being that big, I can also imagine a 2-10-2 version of this... a possible true LMS successor to Big Bertha, especially if it had 3 or four cylinders?..