Okay...... I had a couple of hours free time and had a real good look at the bike. I still can't find anything to suggest a company of country of origin! I looked up at the 105 Shimano parts and they all date to Oct / Nov 1988..... so not the early eighties. There is a faint number on the bottom bracket next to the plastic cable guides which I think reads F9F04981.

I have tried to scan different images to see if the frame paint scheme is on any other bikes but again no joy. Loving the mystery ....