Klaus has sent me so much information that I overlooked this drawing. Here is what I found when I was looking for something completely different.
It turns out that some of my guesses and deductions were fairly accurate, which was a pleasant surprise.
A few hours after posting the original version, I added corrections in this colour. On February 7th, I added further information from Klaus.
Here is the drawing of all the transmission and differential parts. The only additional thing that I wish was shown is the reverse shifter. Klaus emailed me today (Feb 7th) and explained that this is a 1908 SB4 transmission that has a 3rd shifter rod which allows the shift lever to operate all of the gears, like on present day 4-speeds. The brakes, however, are identical to the F2 130 HP. I like the “Fiat” as a raised part of the transmission cover lid, but it would not show on the model, and that is probably an SB4 feature anyway.
Pocher Pacific ~ 1907 Fiat 