Zinsco circuit breakers

Are these a time bomb ready to cause a fire? Recall material? Panel is GTE/Sylvania circa 1954 and I keep tripping a 20A with the portable A/C on and a few other things on that circuit. I'm not ready to drop a G on a new panel but maybe there is an updated breaker that fits this 'plug in' model? I used to deliver this stuff and there were 10s of breaker manufacturers that made compatible breakers. looks like this, breaker probably looks like this

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