I need a headshell recommendation for Technics 1200 GAE

Invictus - right you are, I missed the small m in the first term.  Since you can hold the distance of counterweight to pivot constant by increasing the mass of the counterweight (and nothing else changes), you would need to add the required incremental mass there to the sum I calculated.

@martykl and Z is equal to twice the mass... According to chakster's posted equation anyway.  

@rauliruegas That link is spot on. Easy to follow calculations. Any mass added over the stylus increases the effective mass by the same amount. 

Detachable headshells are a great way to fine tune the effective mass of the tonearm and cartridge resonance. 

@rauliruegas or anyone else, at the risk of beating a dead horse, I want to make sure I understand this.
My SL1200-G has a tonearm with an effective mass of 12 gr. The headshell is 7.6 gr. If I remove the stock headshell and replace it with one that weighs 12 gr. is the effective mass of my tonearm now 16.4 gr.?