Today, I finally got the service manuals for the thing. $400 got me two thick binders of service documentation, plus a copy of the operator's manual. I finally found out how to remove the CRT assembly, and promptly did so (with only a moderate amount of cussing). Once it was out, a bit of looking showed me the problem: some idiot had ham-handedly gotten into the box before I got it (which I knew because of the condition of the front panel), and in the process, broke a power supply wire to the CRT.
A quick solder joint, some heatshrink tubing, and a reassembly later...and it worked just fine. I've now got a very nice piece of radio test gear for $2000, and it's probably worth half again that much. Not bad for a couple of hours' work.