I agree that pickup resonances are largely down to what's going on in the headshell and its interaction with the cartridge.
I found the headshell of my trusty Linn Sondek Basik arm produced slight metallic coloration in the otherwise excellent sound of the Ortofon MC25 moving coil cartridge. Some might say it's all part of the Linn Sondek 'pace & rhythm' character, but I find it sounds much better when properly damped by a penny coin stuck on with a thin layer of Blu Tack. Blu Tack damping is at its most effective when it's the filling in a sandwich between two layers of metal..
I can't readily measure the resulting mass, but the cartridge tracks well at 2.3g and measures within 0.5 dB 30Hz - 18kHz
The small ball of Blu Tack on the end of the finger lift is optional, but I feel it damps another potential resonance. Matt black paint finishes off the whole thing.
Photo attached.
As a general rule, Blu Tack customising looks much more professional when painted matt black.
Martin