This is great stuff!!! My U-40 from my '41 Chevy is currently disassembled and in primer. Just ordered 5 new bearings for it (4 different bearings, two of one), as well as a rebuilt tachometer gear.
Though I assume my truck had the aux. cooler when built, it has been lost on the way. If you know of one available, please advise. Otherwise, I may ask for your help in fabricating one (I don't think they're all that complicated).
My truck (apparently) had no pump governor either, though it originally had the chevy top-speed governor.
Learned a lot about the pump when we tore it appart. Took many photos, but mostly with my iphone, which does not take great pix. Am assembling a rebuild diary like you. Not too far along, but let me know if I can help.
I've got a lead on a batch of Barton pumps (already have two spares) from a fellow, just need to "seal the deal".
We're gonna rebuild the primer, as well. They're my absolute favorite! An oil-less primer, orginally developed in the '20s. American was "Green" before Green was cool!!! It's such an elegant solution.
Keep us posted!!! Your truck is awesome.