A Pontiac casting number of the right era, and the date code is June 19, 1967. Now you really do need to find the two-letter usage stamp. Look on the other tube, on the top and the bottom. There is no hard rule about where they were marked and they will likely be very light. You may need to sand it.
As far as the ratio, you could jack it up and count the turns or pull the cover and count the teeth. The tooth count is also stamped into the ring gear.
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