Welcome aboard the Stovebolt Page.
Specs for the pinion are in the factory shop manual, which is a vital tool for working on these old trucks. Filled with good info, and well worth the $25 to $30 investment. Highly recommended that you obtain one.

Hopefully, in the meantime, someone with a manual will step in with the specs.
As far as the engine color, if you are concerned about the originality, yes, the color matters. On the other hand, it's your truck and you can paint it whatever color you desire. You have to determine if you are going to enter in a show where originality is scored on a point basis. For some people this is important. For others, it's not. One of the advantages of living in a free country.