I'm about to install the cylinder block on crank case. According to partzilla cylinder block diagram it shows o-rings of 67mm and 67.5 mm on the underside of cyl. bl . I do have a set of red o-rings that came with my complete gasket set. The thing is that I can't find anywhere in the service manual any mention of these o-rings. Also I kind of find it a bit odd to install o-ring in that location.