Sorted.
And as has been my experience in so many situations, it came down to something pretty dumb.
Two things I didn't see mentioned anywhere:
1/ Removing the serpentine belt tensioner assembly so you can see down to the timing marks on the crankshaft/block*.
2/ The timing belt tensioner is the mechanical type (with a temperature setting), which I had loosened, and
all that was needed was to push it aside to allow more slack to the belt...
So it was indeed "All quite easy". Ho hum.
Turns out that the crankshaft hadn't moved (once I got a view* of it), and the timing marks were bang on. I hadn't removed the belt from the crank so no need to remove the pulley, and as it turned out, found I was able to slip the belt onto the exhaust cog last of all (i.e. with the belt already on the tensioner).
It also helped that it wasn't near freezing out there (started this job in a heatwave at the end of last summer, kerb-side), so I was able to feel my fingers for longer than 2 minutes.
Anyway, as ever, great to get support here.
Next post will probably be when I need to make sure where some bits came from... I labelled my parts bags, but there are
all these tubes dangling around