Things really started to come together last night. I finished installing the cooling fans, dropped the power supply into the chassis, and connected the 9-slot backplane. No cards and no console, but I consider this my first "smoke test" of the fully assembled chassis and power subsystem. It works!
Exciting days ahead. I have to re-assemble the console, and then I'll drop in the cleaned-up CPU cards this weekend and see what happens. I'm a mite skittish about that.