Thanks very much!

Had been leaning toward Giostra but wanted additional evidence; you have found it.

OP's headset would not have had the Magistroni name as Giostra ceased using this in 1965 and launched the OFMEGA marque in 1966. So if one could find a new one of these in the box contemporaneous with the blue frame it would be so marked. Common for OFMEGA parts to bear no marque or else that of the bicycle manufacturer.

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