After spending a few days checking over things, I put the front panel and knobs back on, plugged the radio in and was greeted with some warm glowing lights.
The two lamps behind the frequency dial indicator both came on, and a nice warm red glow was coming from most of the tubes. Three of them (a 12AX7 and two 6BA6s) were dark though. Fortunately I had acquired all the tubes I needed for the HQ-100 at past hamfests. After replacing the three tube and applying power again, all the tubes were lighting up!
Next step will be to attach a speaker and antenna and see how well, if at all, the radio receives.