North American Design Chief Edgar Schmued incorporated two P-51H Mustang fuselages lengthened by the addition of a 57 in (145 cm) fuselage plug located behind the cockpit where additional fuel tanks and equipment could be installed. These were mounted to a newly designed center wing section containing the same six .50 in (12.7 mm) M2 Browning machine guns as a single-engine Mustang, but with more concentrated fire. The outer wings were strengthened to allow the addition of hard points for carrying additional fuel or 1,000 lb (454 kg) of ordnance. The two vertical tails were also from the XP-51F, but incorporated large dorsal fillets for added stability in case of an engine failure. The aircraft had a conventional landing gear with both wheels retracting into bays under each fuselage center section.
The only difference I have found (apart from it having another plane strapped to it) is that the later models used Allison engines.
This meant that the later models had bulged engine bays to allow for the stupidly large radiator.
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I do not doubt your words, nor your own research. All I'm saying is that atleast 30% of a late model P-82 used P-51 tech for example parts of the airframe and wing.