IMHO, I believe that any Yanmar originally equipped with a two point lift is risky with a box blade larger than 4'. Even a medium duty 4' scraper, when nearly full of gravel, crushed concrete or heavy fill (clay) is quite a work out. I have used a 5' on the smaller models and was always leery of damaging the rock shaft or snapping a lift arm...especially with the rippers down.
gary1611, Not defending or insulting anyone, but I have a different opinion. Obviously those that are well equipped in a shop environment and have the skills and inclination, would not hesitate to make the box blade conversion. I'm sure you could do it (me too) but we sometimes take for granted our God given talents and assume everyone can. It may be a major undertaking for the average Joe and to 'farm it out' would be very expensive (if done correctly).
Personally, I appreciate the experience, input, opinions and ideas of older members, dealers, parts suppliers AND new people with their fresh perspective on the old Yanmar theme. The members on this particular forum seem to be self policing and I haven't seen the necessity for a moderator to intervene since I signed on.
Mark