Short update:

Maccari spring, spring guide and top hat are installed. With a gentle smear of Maccari "black tar" (not sure if this is better than the moly grease that I usually use, but it was included). New breech seal. New red Knibbs piston seal.
10 ft/lbs with 15.89 JSB's. Nice to shoot. Have to wait for new barrel to test accuracy.
It matches Maccari's product description: "nice docile factory power without harshness".
I've read that some C1's produce near-legal-limit-power, but 10 ft/lbs is plenty for me and I think that more would only cause the recoil to be harsher and the trigger to be heavier. For my intentions (plinking and target practice), it's fine.

The replacement trigger has much more creep than the straighter one that was on the gun. I think it doesn't work well with the rest of the trigger mechanism. The sears have way too much engagement and the only way to adjust that would be to remove metal from the trigger sear. So I re installed the "old" trigger, which works great. A very crisp breaking point. I might polish it with Autosol for maximum performance. I swapped the original trigger spring for a ballpoint spring. Now the trigger is lighter (perhaps a bit too light).

The C1 is really easy to re-assemble. Not so much preload, and the trigger mechanism is simple. A great design.