To follow on from Cvairwerks' point, you are either going to start with a BT or start from scratch with existing aircraft parts (possibly BT). Either way, you are going to need to undertake a stress calculation exercise at al, and effectively arriving at he same (replica with other parts) point from opposite directions - but not easy or, I suspect, cheap. It will be like building a new type - ducking the engine power / stress issues (a low power 'sportlike' version) would be another option - but would still be a 'new aircraft' design. Other alternatives would only be to build an accurate replica, or the only easy one I can think of, take a BT, make it a high-back single seater with pop riveted sheeting and then a P-66 with paint...
Incidentally, I just found this on the Flight Global website while looking for something else:
Quote:
VULTEE VANGUARD
THE first Vanguards to be received by Great Britain
were a batch of 100 which had been ordered by
Sweden for her rearmament programme, but when
Norway was invaded in the spring of 1940, delivery became
impracticable and the order was transferred to us ; we did
not actually receive the first one, however, until about a
year later, some 50 of the original consignment having in
the meantime been switched to China, whose need of
modern fighter types was even greater than ours—or
greater than most people knew ours to be, at any rate!
Incidentally, Air Marshal "Billy" Bishop, who later
became head of the Royal Canadian Air Force, inspected
the first Vanguard to be handed over to the R.A.F. in
this country.
Even in those comparatively early days of the war,
however, the performance of the Vanguard was hardly up
to the standard of the best British fighters, its top speed
being 350 m.p.h. at 15,100ft;., and its operating speed
299 m.p.h. at 16,oooft. Its service ceiling, however, was
33,000ft., and it had a useful overload range of 1,190 miles,
as compared with a normal range of 700 miles. Its armament
of ten machine guns was very good for the usual
American idea on this department; it was, in fact, one of
the most heavily armed of all American single-seater
fighters. Four of its. guns were mounted in each wing and
the remaining two in the fuselage beneath the decking and
synchronised to fire through the airscrew disc.
The power plant consists of one Pratt and Whitney Twin-
Wasp 14-cylinder air-cooled radial engine, with two-speed
supercharger, developing 1,100 h.p. at 2,250 r.p.m. at
6,200ft., 1,000 h.p. at 2,700 r.p.m. at 14,000ft., and
1,200 h.p. for take-off at 2,700 r.p.m.
All-metal construction with flush-riveted, stressed-skin
covering is employed throughout except for the fabric covered
control surfaces. The fuselage is built in two
sections, the forward section from engine to cockpit being
of welded steel tubing with easily detachable aluminium
panels, and the rear section from cockpit to tail unit being
a semi-monocoque structure. Flaps of the split trailing edge
type are fitted, and the undercarriage, attached well
out on the wide centre-section, retracts inwards ; the tail
wheel is also retractable.
'O'h, that plan view reminds me of something...
