Then it's necessary to replace these units too:
SU-3 (621) had recoilless gun with low characteristics, because it wasn't produced.
SU-4 (640), 76.2mm K/DPR RG(588) Constructor Kurchevsku was under repression.
KT-27 (620) This SP-gun had no place for gun crew.
SU-37 (627) with 45mm gun (37mm in game), SU-45 (628) had low-powered engine motor.
SU-6 (631) had low-powered engine motor.
Machine translation
PS: I must apologize for using links in Russian.