Ok, a bit more information (slightly contradictory but from reliable sources so I'll just give it as I have it).
The Master was launched in 1983/4 with the main changes from the Mexico (on which Saronni won the Worlds at Goodwood in 1982, there is a reissue out at present and it's gorgeous) being the intricate cast lugs and the Gilco distinctively shaper tube profiles. Later iterations were the Master Piu (internal cable routing), Master Olympic and Master X-Lite (thinner walls so the tube diameter increased). Not sure when the straight Prescia fork was introduced but have read that it was introduced at about the same time as the original Master. So looks like I was at least a year or two out with my original guess but with the curved blade fork I think it probably is an early Master.
Thanks a lot. Very interesting information. I really appreciate your help.