"That said, I doubt it is likely. It did first fly in 1938 and was introduced in 1942, but its construction - by what I've found so far, appears to be more typically flush, heavier military. I found a few pictures on Wiki so far - lots of flush rivets on outer skin.
It did have lovely lines despite other challenges to its performance."
Quite an innovative design for a pre-WW2 plane Jeff, mid engine to allow for the machine guns to be installed forward of the cockpit, tricycle undercarriage but, shame about the performance and inherent problems with the skin stress. Fully flush riveted as you noticed and nice streamlined lines as well, good looking plane.
From a recovered P-39 project regarding problems with the skin
During testing and combat reports, the one thing the Soviets were discovering was that the P39 suffered a structural weakness of the rear fuselage. After thorough testing, the Soviet LII (Flight Research Institute) and TsAGI (Central Aero and Hydrodynamic Institute) recommended a number of improvements to be undertaken at repair workshops from mid 1944.
These were recorded as: -
Defect and modification. - Twisting of rear fuselage and skin deformation.
All Q models up to and including the Q21 to have the following.
a. Two additional skins around radio compartment hatches.
b. fuselage longeron reinforcing member
c. two supports to forward tailplane spar attachment joints
d. two plates to reinforce the port forward fuselage beam.
Items a and c are clearly visible on ‘White 23’. These skins have been added over the red star and have covered segments of it. Whether or not it was deemed important, the star was not repainted.
All Q series models were to have the following work undertaken to the fin.
a. reinforce fin leading edge with additional skin.
b. add third fin/fuselage attachment point.
c. reinforce the forward and rear post with additional profiles.
d. additional plates at the middle of the rudder hinge.
http://lend-lease.airforce.ru/english/articles/sheppard/p39/I was aware of these problems as I have read up on this model many years ago and wondered if the problems were due to the mid engine arrangement adding unexpected stresses along the length of the fuselage when manoeuvring.
From a P-39 restoration project regarding the riveting
"In fact, what shines through every facet of this 28+ year project is the ingenuity Ian applied not just to replicating the work of "Mr Bell and his many thousand work force of WW2" but to the very design and building of numerous tools. The P-39 features an external skin flush riveted throughout. These rivets require 'countersinking' and when holding thin metal STRESSED skin in place, this means deforming the inner edge of the hole - an operation called "dimpling".
http://www.qaww2.com/p39-project.html