I believe Q66/Q67 form the TX switch for the RF power amp driver Q60 and Q62.
What usually goes wrong is a driver shorts (i.e. Q60 or maybe Q62) and that overloads/cooks the TX switch Q66 and the voltage just collapses, as you are seeing. So that section likely works fine, it's just being overloaded.
If you are measuring continuity from the switched power bus TP7,8,9 to GND, a multimeter will charge all capacitors on that which can take several seconds. D94, C260 etc. will interfere with that measurement so you must isolate the part you are testing.
You could just pull Q60 out or lift one of its leads and then diode-test it. I would do that, and for Q62 as wild guess one or both have failed.
The purpose behind three testpoints TP7, TP8, TP9 is for open-circuiting them and then measuring current flow at each one.
When setting bias current, say for Q62 when adjusting VR13, it's 10mA with no modulation, across TP8-9. For Q60 when adjusting VR11+VR12, it's 50mA each with no modulation, so 100mA total across TP7-9.
If it's easy to open-circuit a TP7-TP9 bridge, then that's another method to check continuity to GND on Q60 without the rest of the circuitry in the way. I don't know what the PCB looks like, if these are solder-jumpers or what. The service manual has some special board "short pcb" though.
edit: Q66 is a 2SB754? That's fairly huge 7A transistor but not powering the final power amp?