Thank you for the helpful suggestions! I found some time to play with it this evening. Turning the brass screw clockwise/counter enabled me to find a sweet spot for maximum vibration. If I held the light just right, I could see a very slight wave pattern on the surface and a few bubbles generated at the bottom. Hopefully it will improve after things are cleaned and parts updated.
I also pulled the tubes to look at the pins -- they looked remarkably clean, like brand-new clean. Using my voltmeter, only two pins showed continuity. I think this result is expected based what I've found online. Without access to a tube tester, I'm not sure what else I can do to test them further.
Per your suggestion, I also made progress in bending the drying cup back and decreasing the wobble. I'll try again next week, but am confident it will eventually be useable at max speed.
Work will be getting in the way for the next 5 days, but after that I should have time to invest in the project. Thank you again!