On the subject of the Soviet Union and the DC-3, Douglas gave the Soviets a licence to build the type in 1936 and the deal was that Douglas would supply examples to the Soviet Union for study; 21 were purchased and sent to Russia (some sources say 18), along with drawings, which caused delays to manufacture since the Russians worked to redo them from Imperial to Metric measurements. Engines, wheels and tyres, propellers and other ancilliary equipment were locally supplied, some of which had been built under licence from the USA at any rate, including the Shvetsov M-62 engine, which was a derivative of the M-25, which was a copy of the DC-2's Wright Cyclone. The Japanese and Dutch received drawings as well and initially had trouble transposing them to Metric that the first Japanese example completed, by Nakajima was assembled from US made parts. Showa production and subsequent Nakajima examples were built to Japanese tolerances, as were the Russian ones, which required extra strengthening to meet official standards.
The PS.84/Lisunov Li-2, although looking like a DC-3 was a very different airframe in many respects. Structurally the airframes were the same, but Russian research institutes insisted on heavier gauge materials and beefier structural elements to cope with their requirements for the aircraft. Built as a civil airliner and specifically military roles of transport and bomber - not just a conversion of existing transport aircraft, the bomber variants were built as such on the production line and incorporated internal bomb storage, bomb aiming positions and other things conventional transport DC-3s didn't have.
Douglas did only supply construction information and couldn't stipulate what the machines were to be used for, not that the Soviets would have listened anyway. A large number of Soviet engineers from aircraft factories and research institutes went to the USA to study the Douglas production lines, which was part of the deal and on their return to the Soviet Union began the process to get the type built since US production methods were far in advance of Soviet ones at the time. The entire process was of course different to how Western manufacture of aircraft took place. In the Soviet Union a requirement was issued to the research institutes by the requisite government department (strictly speaking, all the aircraft companies and air force and civilian research institutes were government departments, which is where the differences between the two systems reveal themselves), who released specifications and from those, different factories, i.e. aircraft manufacturers would then be chosen to build the aircraft required, based on the research institute's findings. This was all done under governmental guise, the appropriate civil or military government department making the final decision as to who was to build the aircraft based on the factory's suitability and experience.
At the time, only Tupolev and Ilyushin had experience in building all metal airframes, but following the recommendations of the defence department, Plant 84 at Kymkhi, run by Pavlovich Lisunov was selected to build the DC-3, with Vladimir Myasischev, who at that stage had worked for Andrei Tupolev and had yet to form his own firm, as project leader.
The tricky thing is, with the modifications made to the PS-84, and subsequent DC-3s supplied to the USSR, it's hard to tell them apart. This is a Douglas built DC-3 with Soviet engines in China (at the China Aviation Museum outside of Beijing).
DSC_6667
Compare that image to this one of a Lisunov Li-2 civil transport and minor differences become apparent (at the Civil Aviation Museum of China,
in Beijing - not the same place as the aforementioned and better known museum).
Li-2 1