Be careful with shorting clipped wires to ground (first message). You are probably also missing D126 which is soldered directly between two switch contacts. If you have a later S/N 15920-up then perhaps missing are also some resistors (R125, R127) when these are also soldered at the switch. In my older 2B67 4 wires leave the switch contacts, plus a short blank wire to the Ready light. Note that the switch has been removed in the photo at page 7-4.
To R135: separate wire via plastic support (4) at page 7-4. Yellow on white.
To R126/Q124base: separate wire to ceramic strip, 8th notch from front. Yellow on white.
To Q124emitter: in wire bundle. Yellow on white.
To ground: in same wire bundle. White. The two selector contacts are blank wired together and to the white wire. (No ground wire to to switch body or attachment screws.)
To imitate Normal mode you might ground the wire to R135 via a diode (substitute for D126, conducting to R135).
From the schematic it looks like the missing switch would just lead to the scope always triggering in Normal mode, rather than single shot. Might be nice to have single shot, since I assume the storage mode is designed to store this. Though this is a much less used feature.
Googling the part number of the switch did not turn any up yet. Will have to see if stability adjustment fixes it first.