If you look at a old (pre GTE Sylvania)Zinsco,it will say "Zinsco Electrical Products Los Angeles Calif."and one of those really old clay pigeon substitutes,will say "Magnetrip".
P.S. I suspect they had more national distribution after GTE bought them in the 1970s. They were very popular in apartment buildings,trailers and other structures wired by bottom feeders.
The best thing about that Zinsco Panel is: The plaster job that surrounds it. This guy cared enough to insatll metal chanel around it so he wouldnt' plaster the door shut with the new finish depth.
Cutler Hammer would have been a non-choice in the '60s. The type CH/CHB breakers weren't introduced until about '72 or '73 Even then, they were considered by many as too new to be trusted.