With Hirata and Yano.
We tried to replace the heavy top plate in F0 keystone assembly by a new lighter one. However, after immobilizing the keystone in vertical and yaw we realized the existing assembly uses socket head screws and not countersunk head as the in the new design. We didn't install it but we will once we buy new screws.
The new design was based on the F0 prototype 3D-CAD, which uses countersunk head screws.