During cranking, the con rod ends (where they attach to the bellows) weren't quite smooth enough for my liking - if I tightened the end nut all the way, there wasn't enough play for the bellows arm to slightly swivel/rock between the leather washer, and if I left the nut a little loose, I could feel the clunking as the rod reached its end travel dead spot.
Turning the organ upside-down, I first dropped a 1/4" brass washer onto the rod. The rods are nested inside brass tubing, so the bigger diameter tubing keeps the washer in place. Next I dropped on a short spring, followed by another brass washer, then a leather washer. Next, I put the rod through the bellows arm, put on another leather washer, another brass washer, and finally a nylon locknut which I tightened down so that the spring was just less than fully compressed.
I put a fake brass coating on all of the steel parts.
Now the con rods are nice and snug, but still have a little bit of spring-loaded flexibility.
Even though I don't have the crank handle made and installed, I still wanted to do a preliminary pressure test on the bellows/reservoir assembly.
I think it's OK, but I find conflicting information about how much pressure I should have and how long the pressurized reservoir should stay up before fully collapsing.
I originally was getting about 8 and a half inches of pressure, but I adjusted the spring back a little to lower it somewhat.
Here's the test, using a manometer set at inches of water:
