Grasscut 255-8

Hi

I want to fit a Grasscut 255-8 on my FS400.

I have the mounting kit 1 (4119 642 7600, 4119 713 3100, 4128 713 1600) see picture

This kit works for Bruschcut 225-3 but the Grasscut is thinner so the splines shaft sticks out of the guard ring so the ride plate does not clamp in the blade. Which spacer do I need?