Call me crazy, but looking into applying the conversion to superfluous Mach 2 kit.
That caused me to compare Airfix and Mach 2 offerings, and the differences prompted a measurement against the original drawings in the BAE Systems archive.
The Airfix kit is overscale by about a foot in span and length. Whoever said above that the nose of the Mach 2 kit was not short appears to be correct as the distance from the leading edge of the wing to the nose is similar, although the Mach 2 cockpit bulge is clearly in the wrong place and open to replacement with one of the spare Airfix parts. The problem with fuselage length is aft of the wing, by over 4 scale feet, and surgery probably needs to be where the section is closest to parallel in the wing area.
Still trying to work out if I am wasting my time....