Sorry to drag this thread back from the dead, but a G.P. marked seatpost is for sale here on BF which can positively be identified as a 3TTT Gran Prix post. It is only marked with the script G.P., which the seller astutely correlated to the model name.

So perhaps not Gipiemme after all.

Velobase 3TTT Gran Prix entry: http://velobase.com/ViewComponent.as...m=105&AbsPos=0

Photo of seatpost: