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My slightly annebriated new years troubleshooting advice:
You are right, some of your B+ voltages are well outside of tolerance, however those rails are derrived from other rails that are also not dead on spec (and things may not be loaded correctly) which may give GIGO data.
No tubes should be pulled with the H out screen and plate (the top lead connection) disconnected. The fly will not (or at least should not) be loading the B+ in this state. The flyback typically only loads the highest B+ rail (through the damper)...So if it is driving you nuts that all your B+ rails are high and you have a variac you can cheat your way to normalizing your B+....To do this connect a DMM to the 405V rail on your schematic and dial your variac till that rail reads 405V then you can accurately access how screwed up your lower voltage B+ rails and circuit voltages are*. This is probably the ideal state to do what you should focus on: Getting the H osc on frequency with test instruments, getting the osc amplitude and waveform up to spec and most importantly getting that signal delivered to the H output grid and developing negative H output grid voltage within 10% deviation of spec. Only when you have a decent approximation of correct H output grid voltage will it be safe to reconnect the H out plate and screen (that is a $25+ output tube so I don't advise running it outside of specs). When you have good H out grid drive you should be able to put the circuit back to stock connection and then have HV, horizontal sweep, and other working-set-like goodness (though shorts on the fly side could hamper much of that if present).
If the osc is not behaving and is powered by a lower B+ rail that is way out of spec even with variac normalization of the high B+, then what you should do is trouble shoot everything on that lower rail and try to get that rail properly loaded by working circuits.
*This may lower your heaters and make marginal tubes show their uglier sides.
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