Weren't no
razor-back Mustangs, only P-47s.
When did people start referring to the original Mustang fuselage profile as 'razorback'?'
it's neither humped in profile nor sharp in cross-section. To me it's always been P-51(A, B, C)
and bubble-topped D, with no reference to profile necessary on anything other than the D.
I've even seen it used in reference to Spitfires!, which is truly incorrect, Spits are normal
and low-back/cutdown for the bubble canopy versions.
The term is really only correct for the pre-bubble P-47s as the canopy fairing was indeed
humped in profile, along with being sharp in cross-section, another inheritance of its P-35
grandparent.
Anyhow, as to the bird in question, other sources, including NAA order number/production lists,
refer to order number NA-106 P-51D, no block number, (not P-51D-1, none of that block were built)
as being two NA-102 P-51B, 42-106539 and -106540, the two aircraft mentioned in the article, modified
to test the new canopy installation, the only mods were those required to mount the bubble canopy and
new windscreen. No D-wing or six-gun modification is mentioned.
The first aircraft modified to the bubble canopy was NA-102 P-51B 43-12102, however it was not
against order NA-106.
Having looked at the, single, photo of -106540 from the article (it's available at their site), I'm not
convinced that their statement that it shows a
three gun right wing is correct. It appears to
show the shorter ammo bays, as standard on the B/C, not the longer ones as fitted to the D. Now is
it possible that they trialled a three-gun
installation? Sure, however that wouldn't require a
three-gun wing. Also the wing really isn't clear enough in the image to make that determination.
I think they're creating a mystery where none exists, I believe it's simply a photo of 42-106540
before it was modified to bubble canopy configuration.
NA-102 P-51B/D 43-12102