Locking flywheel

[Ben]

Currently trying to replace cambelt on my rallye (although it's an early 6 engine) and am struggling to find where to lock the flywheel off. I've got a locking tool with 4 teeth and a slotted bit for a bolt to go through. I can get it through the top of the gearbox just to the right of the starter motor but there is no hole in the box to line up with the slot in the tool..

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Thinking of removing starter and using one of its mounting bolt holes, but I've not read anywhere about having to remove this so wondering if I've missed something?

Thanks