I don't know of any way to determine the pressure angle easily. Maybe somebody else does.
You can calculate the diametral pitch (assuming it is not metric module) by counting the number of teeth, adding 2, and dividing by the o.d. in inches. Things being what they are, it won't come out exactly even, but if you get something like 16.06 or 15.92, you can probably assume it's 16 diametral pitch.
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