The 2013 C59's are now fitted with the Acros The Clamp headset shown below;

http://www.colnago.com/colnago-integrated-headset-y/

The stack height of this set up is approx 5mm more than i need on my correct frame size. Can i use a standard low top cap and expander plug with the headset cup and bearing from "The Clamp" as supplied with the frame?

I can get the correct fit by using a lower rise stem but I would prefer to have the lower stack height...

Cheers

Rich

Assuming there is nothing odd in the fork steerer construction you should be able to switch out the top race (I hasten to add that I've not got first hand experience on this, I'm basing this on the specs online)

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try colnagos facebook page or colnago.com they have been very good to me in the pastt with any question