Was looking at my father’s panel today and besides a multitude of other problems (double taps, triple taps ect.) I believe this to be a problem panel. It was installed in 1979 which would put it in that Era. Bus Bars are not copper but I don’t believe it’s the blade type design. looks like the hook in on a flange on the left hand side and attach with a screw on the other.
The label is very faded, all I could make out was sylvania and gte
Breaker to bus bar attatchment, picture from top.