Just to finish this off, arrived and let it run through its updates (came with W8.1). Then fitted a spare SSD in place of the spinner (fiddly but have had worse!), and put the spinner in a caddy in place of the DVD. Installed W10 from USB, all Windows and driver updates done, and it runs lovely.
Just as a note – as I had read when I clean installed Windows 10, it activated automatically from the embedded (W8.1 ) key. So although the official free update and the later assistive update have officially eneded, worth a try to upgrade an older windows version without buying a new license – seems like MS are still happy to unofficially update gratis.
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