They would all be involute form. The alternate tooth form to involute would be cycloid. Both share a constant velocity motion, but the involute will tolerant a wide range of shaft center distance without affecting the velocity.
20 degree pressure angle seemed to be more prevalent prior to WW2, and 14.5 more common after that. I have not checked the mid-thirties gearboxes, but timing gears from the EW through the mid-thirties used 20 degree pressure angle. There was something that did change part way through the 4-speed gearbox's evolution, something to do with the tooth form, that prevents the third generation gears from being mixed with the second generation. But I seem to recall hearing that one can swap out the entire contents.
Stub teeth, are as Jim mentioned, a stronger variation that found favor in transmissions. They are formed by altering the pitch diameter. All the systems I know of, American Standard, Fellows, and obsolete Nuttal system are 20 degree pressure angle. Basically the pitch diameter is shifted outward, the tooth depth made shallower (or both.) This makes the teeth 'stubby' and stronger, at the expense of a few other functions. The alternative, particularly on smaller pinions with minimal number of teeth, would be a tooth profile with a weakening undercut at the root of the tooth. The ratio is unchanged, since that is a function of the number of teeth. The 12/14 designation is one used by the Fellows system. The numerator is the pitch used to calculate pitch diameter, tooth thickness and number of teeth. The denominator is the pitch used to calculate the depth of the tooth. The other systems use alterations to the gear calculation constants for tooth depth.
And yes I know, this still does not tell you exactly what form your '36 gearbox uses!
-Doug
