Update: got a ringspanner; used the starter motor as recommended - job done
(almost a month ago actually)
Alas, three of the bolts through the water pump/timingcover sheared off (actually I think two were sheared previously and stuck back in rather than replaced), and as there's evidence of weeping on the timing back-plate/engine-block gasket, I'm currently trying to remove the backplate to replace the gasket and see if I can get the stumps of the bolts out - which involves removing all the sprockets (done) and trying not to mess up the timing
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Ruddy landrovers - it's a good job this is a 'project' and not an everyday vehicle.