According to an article I have from Scale Models international, Dec '96, I can give you the following gen;
Pre WW2, no DC 3 had the freight door, & only some, notably American Airlines, had a door on the right, probably a hangover from the DC 2.
Pre WW2 most DC 3's used only the single row Cyclone engine, the twin row R 1830 was introduced on the C 47, though some of those used R 2000's. (Check out the South African R R Dart turboprop conversion !) I've even seen pic's of a Trimotor DC 3.
Side windows can vary, and the US Navy R 4 had a different fin &, I think, a fuselage 'plug' forward of the wing. this was used on some DC 3's too.
Russia reverse engineered the C 47/DC 3 to produce the Li 2, probably using the same engine as used in the An 2. And how about this for versatlity, an article in
Aeroplane Monthly or Flypast a while back, showed how Czech film makers altered an Li 2 to produce a very convincing Wellington! I don't think it flew though.
So yes, Quagmyre, it's probably the same kit, though the engines/cowlings may be different.
And if anyone is interested, the SMI article compared the Airfix, Italeri & Esci DC 3's in 1/72nd. All have faults, but it turns out the Esci is most accurate, except for the props.
Also, yes, the WW2 luftwaffe used DC 2's & 3's, usually ex KLM. Japan had them too, they used them as transports & used the wing design for a Bomber.
Pre war, China airlines had an accident in one of their DC 2's, and replaced one wing using the bigger one from a DC 3, it still flew fine!
There is only one replacement for a DC 3, & that's another DC 3.
Hope this helps.
Pete