that's the Decca advise to the Super Gold owners. The tonearm and the after market headshell you choosed for your Decca cartridge goes against ( both. ) the manufacturer advise.
Your FR tonearm is a very old non-damped design. " Rings as a bell ". Your choosed headshell is an non-damped design too.
In both cases that's means a way higher distortions that a well damped tonearm/headshell design.
In the other side its VTF mechanism "" rings as a bell "" too.
If you have not other alternative to mount the Decca cartridge then make the VTF set up as if the tonearm design was not dinamically by design but static one, using exclusively the counterweight to make that VTF set up with the additional advantage that the counterweight will be nearer to the tonearm/bearing pillar.
Unfortunatelly you own one of the worst tonearm and headshell designs in those regards.
Now, due that the vertical compliance is very low in the Super Gold could be better that the resonance frequency stay very close to 10hz and if posible in a diferent tonearm/headshell.
Decca manufacturer knows very well its cartridge designs and that's why they give precise advise on what kind of tonearm mate well with it.
Of course we can use any tonearm and the Decca will " sound " but ( at least for me. ) that's not the priority but try to achieve the best quality sound/music performance level we can.
Regards and enjoy the music,
R.