Just finished reassembling. The tool was perfect.
Conflicting advice on sense of thread repair.
Couldn't find the replacement part (RH crank, spider and spindle) from Shimano and the whole kit (inc rings and bottom bracket) was €72 or more. Easier to find the version without a chainguard. Local bike dealer agreed to split a set and sold me just the bit I needed for £30, so I kept the old chainguard with the old outer ring.
So, thanks to Warlands Cycles in Oxford, and thanks to all of you.
Jonathan