@lewm, Yeah, those 1970’s Deccas were so shoddily constructed that people did all kinds of things to optimize their sound, including the risky internal adjustments you made. The current Londons are much better built.
The Decca/London cartridge design is unlike any other, even the few that share with it having no cantilever. It has a single lateral sensing coil, and two vertical ones (out-of-phase with each other). The electrical relationship between the lateral and vertical coils is what produces the cartridges’ stereo signal. In the mono version of the Decca/London, there is but a single lateral coil, so the cartridge is incapable of producing a stereo signal; it is a true monaural design. I’m gettin’ me one!