Hi Larry!
1) these designations are long forgotten and were applied rather randomly when the Germans discovered each new variation on the T-34.
2) this model was created when mating a stamped turret to a normal model 43 hull, and I think I remember around 1k or 2k were made along the more usual cast turrets.
3) russian battlefield is the usual answer (
http://www.battlefield.ru/index.php?lang=en )
HTH