What was the projection used for the Soviet Topographic Maps? http://maps.vlasenko.net/smtm50/k-37-072-1.jpg i am trying to georeference a map from Georgia. I believe the projection used was GK (3 degrees) with a Pulkovo datum (epsg 2530 in the case of the map above of the Georgian city of Poti)
For such a small area as that the projection probably won't matter, the earth is essentially flat at that scale. Just define a few reference points in whatever output coordinate system you want to use (Some UTM Zone, maybe) and that should be fine. I doubt any precision error will be down to not specifying a projection, it'll probably be swamped by the referencing, cartography, surveying, and scanning precision errors.
Different story if you are trying to georeference a map of the whole of the Soviet Union though.