Killed the double pole breaker and none of the other breakers went
dead.

If it were a split buss panel, you would undoubtedly have more than a single
double pole breaker

It is entirely possible that the service was installed improperly,
especially if the meter equipment and panel are of a mid 60's vintage




I will try to anticipate your next question.

No, I will not send you the box because you don't believe it's not a
split bus panel. :-)

Andy