I’ve seen a few Zinsco panels in my time, but this was a first. At first glance it looked like a split bus, but in fact, it was a parallel service.
A single drop split to two sets of SEC’s. I’m not sure how it looked behind the meter, but two sets of conductors fed two different breakers - one 70 amp and one 40 amp.
The 70 amp breaker supplied the general house circuits and the 40 supplied the condenser for the A/C.