Here's a summary of today's project. I thought I'd post it here in hopes that it helps someone else.
C721 center shriveled up
DS563 and DS564 do not light up
One filament wire from T550 broken at PCB
Basic measurements found abnormal:
+5, -5, +32 V all zero
Replaced C721 although it tests okay at low voltage
Resoldered both filament wires to PCB
Removed R523 and checked nearby components
VR524 DMM diode test 0.45 V one direction, 0.87 V the other.
Conclusion: Current through C522 probably took out R523 and VR524 and blew F736
Remedy: replaced all three of those components and F736
DS563 and DS564 flash at turn-off, otherwise dark
-2kV test point gives 1980V under 4 megohm load
Unplugged CRT HV lead. At socket, 7.6 kV under 13 megohm load
Beam appears...everything works!
Note: neon lamps slowly lose their gas. 40 years seems to be enough. So if they're dark, it doesn't mean you don't have high voltage. Be careful!