With the A/C package tray in place, I can re-install the battery tray (I can do the remaining plumbing and wiring without those interfering). I put the battery tray back and installed it permanently with screws and bolts. Then, before putting the battery back, I installed the pitch servo. Rather than depend on the star washers, I safety-wired the bolt heads, which was super hard to do but looks much better. Then I attached the servo linkage to the belcrank and reinstalled the pushrods and tested the elevator motion from the stick (can't test the servo until it is wired in).
Next I put the battery back and found that the condensor interfered with a wrench for installing the battery keeper. Solution: drill and slot the rear of the keeper to fit the already installed bolt, then finish the attachemtn with the front bolt. After restoring all the wiring and testing, I installed the oxygen bottle to be sure it didn't interfere with anything. Success!