The Circuit Breaker can be the first or second element in series....
Install L or T type current limiting fuses with an appropriate rating: have an EE design it.
If the bussing permits, install a different breaker.
With such an old piece of gear: scrap it.... (I can't believe that old breaker is still passing its tests.)
Alternately, feed the existing service from the new installation. Re-engineer it.
Blame the extra on the Poco. Not your fault.
