Measuring the response of the filter in the 431 might be instructive Whoops ,
or anyone else with the same mic might be interested in doing it .
Its does seem likely the inductors are in a symetrical arrangement ,
they look very much like common mode RF chokes ,
theres lots of off the shelf options with those components nowadays ,
Applying the MD431 technique to a Shure 58 makes a lot of sense ,
, creating a tiny sub pcb to fit inside the mic itself looks tricky ,
, keeping the mic stock in any case is more useful ,
Id envisage everything mounted up in a DI box type enclosure ,
switchable HPF, attenuation and mute switch ,
a broad cut to the mids ,like Rossi did, could likewise be arranged on a switch ,
In another thread I mentioned the Sennheiser MZA-14 powersupply ,
trimming out the phantom power part of the circuit leaves you with a nice active LPF and pad ,
the only extra tweak is getting that circuit to run off externally supplied phantom power .