Good morning Stefano,
I replied to you twice, so looks like my email are going to your spam box.
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Here is my answer to your email:
Yes this is a picture of my boat.
I did not know there was different shaft.
I just look back at http://nikimat.com/auto_prop_h6.html
on picture 19 (you can do a right click, save as to see the picture number), you can see the Spur’s rope cutter is fixed on a portion of the shaft that is flat (or horizontal).
On photo 56 you can see the reinstallation of the Spur’s.
Here is the Spur’s you need: http://nikimat.com/spare_parts_spurs_marine.html
But prior you need to make sure the Amel part number: 3184 which is: VE DE COUPE ORIN 20 mm ACIER 18/12 MO / V bolt for rope cutter (steel)
As it will hold the bottom part of the rope cutter.
I suspect the plug that hold the transmission oil doesn’t look like this on yours.
I would make sure it is at the same location than on mine and that there is sufficient place on the shaft as well…
Hope that helps… Alexandre