LeCroy LC684DXL oscilloscope -- PS9611 power supply repair notes/questions

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I have owned the scope for several years and was using it regularly until it made a dull pop while powering on, then completely dead. Schematics are available in the service manual on the KO4BB site and I am attaching a screen shot of the relevant section. I did not find a part list in the service manual but U3 is UC3845, U4 is LT1249, U5 is TC429CPA, Q4/Q5 are STW20NB50, and CR19 is STTA1206D.

Parts I initially found bad were Q4 and Q5 (main PFC switching transistors -- one had bits of the package blown off), CR19 (main PFC rectifier -- shorted), R72 and R60 (gate resistor and gate driver power filter -- both visibly toasted), and the gate driver U5 (some pins shorted to supply rails). After replacing those parts the supply attempted to start but both the line input filter module and supply made some unhappy noises and the inline 15 A breaker/GFCI I was using quickly tripped. With one side of F2 between the PFC and primary side of the transformer lifted the behavior was the same. I was worried about causing further damage so I switched to powering it from a lab supply with voltage set just above the startup threshold, approximately 130 V, and gradually increasing the current limit I was eventually able to observe the PFC output +VDC going above the 375 V setpoint. (The highest I saw was over the 450 V rating of C94 before quickly shutting it off.) The overvoltage was due to one of R85/R54 (249 k each) being open, breaking the PFC voltage feedback loop, and with them replaced the scope is working again and has survived a few dozen power cycles and several hours of operation. I also replaced C94 as a precaution even though it seemed fine since it had been driven above rated voltage several times.

Two observations: The TVS device Z1 shown in parallel with C94 on the schematic was not actually installed and no evidence of removal -- looks like it was omitted when the board was originally assembled. Also, the series pair R85/R54 that had failed open was apparently a modification from the original board layout which has only a single footprint, R54. The modification to two series resistors looked professional, probably done originally when the board was assembled, but maybe evidence that there had been some concern about the voltage/power rating?

Some questions:

The coupled inductors L13 are on a large toroid with turns ratio I estimated at roughly 10:1 left:right so it seems like the left side of L13, Q4/Q5, and CR19 should function basically like a standard boost converter, but what exactly is the purpose of the right side of L13, CR20, CR21, and C95? Is there a name for that topology?

Does the failure chain R85/R54 open -> +VDC overvoltage -> CR19 reverse breakdown and fail shorted -> remaining damage caused by C94 discharging through Q4/Q5 make sense?

The original Q4/Q5 and CR19 parts appeared to be not readily available so I replaced STW20NB50 with NTHL095N65S3HF and STTA1206D with IDH20G65C6XKSA1, do those substitutions look reasonable?