Is1 and KV85s were just stopgaps before the Soviets came up with the t34-85 and the IS2, don't think they should be added to the game.
KV-85 - produced 148 (all produced tanks were used in combat in 1944)
IS-1 - produced 130
Ostwind - produced 43-45
SturmTiger - produced 18 +1 prototype
If required Ballance, why not?