Previously, SEA answered the FAQ "...can the KTR-953 and KAC-952 be mounted in different locations in an aircraft". The answer to that question details the service bulletin (mod) levels that each unit must have incorporated for this installation scenario to be possible.
In addition to what these service bulletins offer in the way of installation flexibility, improper performance and actual unit failure can occur if the units are mismatched. KTR-953 units with SB 8 should only be paired with KAC-952 units with SB 9 & 10. KTR-953 without Mod 8 should only be paired with KAC-952 units without SB 9 & 10. Southeast Aerospace has actually seen units fail in the field when mismatched in this manner as well.