You said it yourself, you're not an GIOS expert @anidel. And since you're not, and since you aren't here to buy it, maybe you should refrain from telling me or anyone else what your best guesstimate tells you, this is worth. People who know GIOS and know how to appreciate rare italian craftsmanship from the eighties, will make me a decent and legitimate offer.
Until that happens, I think you should take another look at the pictures and enjoy the completely original frame and fork and its details like pantograph engravings, cromed fork and replaceable dropouts - details you don't find on a namebrand frame anywhere at £200.
The only thing that is wrong or misplaced on that frame is the Chris King headset. But I might take it of and adjust the price accordingly or offer it with a Record headset instead.