What is a Russian BA20ZD Armored Railcar ?
Google search.
scroll down about 3/4 of the way: http://mailer.fsu.edu/~akirk/tanks/pol/OtherPolish.htm
Also a line drawing: http://mailer.fsu.edu/~akirk/tanks/pol/Pol-Ba20m.jpg
How accurate is this information? Not sure, but unless you can find a book on WW2 Polish/ Soviet armored cars, this may be as good as it gets. Good luck modeling a vehicle with no known pictures; although, that does allow for a lot of artistic license.
EDIT OK, seems like there are some pictures, just no war-time period pictures. try wiki: http://en.wikipedia.org/wiki/BA-20. Again: accuracy? It’s wikipedia, you be the judge.
It’s an armored car body put on a GAZ AA truck chassis. The GAZ AA was a Soviet copy of a Ford AA. The Soviets also stretched it into a 4x6 chassis called the GAZ AAA, which, in turn, based a number of Soviet 4x6 armored cars: BA-6, BA-9, BA-10…
I expect the “railcar” part indicates the road tires were replaced by railroad wheels.
I’m building a BA-9 in 1/72 by the Ukranian company UM. It’s a very nice kit. It should be done in a week or so, I’ll post pictures then. The BA-9 was based on the AAA chassis and had a turret with a DShK 12.7mm machine gun in the turret and a DT 7.62mm machine gun in the right side of the driver’s compartment.
UM produces one variant with the railcar setup.