The power-up continues...
Checked the screen, grid and cathode voltages on the 6BG6 socket, and everything looked "safe. Hooked my scope to the grid, and got a reasonable-looking but low 30Vpp drive signal (service data says should be ~40 Vpp).
Things are looking pretty good, considering all the original paper caps are still in!
Shut down power, installed a 6BG6, and hung my DMM on the +225V rail. Made sure the 1B3 lead was in the clear, and applied power. Took a neon test probe (NE-2 bulb taped to a plastic stick), and held it near the 6BG6 plate cap. Bulb lit fairly strongly. Waving it near the 1B3 plate lead, it got much brighter. Lots of high voltage RF being made. No signs of arcing/corona/smoke from flyback. Looking even better...
Stuck in a 1B3, and connected HV meter (Fluke 87 and 80K-40 HV probe) to CRT anode clip. Applied power and....whole lot of nothing. About 4V if the meter can be trusted that low (.004 kV was the reading). Bringing back of hand near end of anode wire gave no static to hairs, and bringing a grounded screwdriver near it gave nothing at all. Bringing the screwdriver (now ungrounded) near the 1B3 plate cap (briefly) drew a 1/2" long RF arc. We have HV AC, but no DC.
The 1B3 I have in it checks good (on a TV-10D/u) but it has a internal insulating coating that obscures the filament, so I can't see the filament glow. Will have to dig up another one to try, I'm sure I have a few of them kicking around.
Only other possibilities I see would be an open resistor under the 1B3 socket (R187 or R167) (somewhat common), or a shorted HV filter cap (C142, but these mica or ceramic "doorknob"caps are usually pretty reliable).
At this point, I'm going to go ahead and swap the 1B3 to rule it out, and then forge ahead on the recapping. Have all the needed caps ready to go in. Would have liked to get some light on a CRT, but probably pushing my luck running this thing much at this point. The 1B3 socket resistors and the HV cap all require at least some disassembly of the HV cage to get at, so will investigate this area after doing all the underchassis work.