Hello Michael,
I founded this data on axishistory forum. The guy lists several documents from "The central Archive of the Ministry for Defenses of the Russian Federation", that are his personal findings. There are several documents listed, all confirming this data.
Check this links:
http://forum.axishistory.com/viewtopic.p...&start=105
And next page:
http://forum.axishistory.com/viewtopic.p...&start=120
Look for quoted text in posts from "Yuri"
Also as I'm aware tank brigades at that time usually had around 30 T-34s and 20 T-70s, and in current OOB it looks like 20 T-34s and 30 T-70s so it seem logical also.
milicko