Class 60 gray iron might be a difficult animal to produce - class 50 is usually at the top end of the gray iron as cast range. Higher tensile strength gray irons need low carbon equivalent iron with supplementary alloying to reach the high tensile properties and these are prone to carbides especially in thin sections such as sleeves.
Thin section cast iron sleeves quite often display a microstrucure that is undercooled, type D graphite which will be associated with ferrite unless pearlite promoting elements are increased (Cu, or Sn). The undercooling can be an indication of the risk of carbides in the microstructure. The Type D graphite with associated ferrite
will limit the tensile strength and class 50 would not be likely. Some of these sleeves are centifugally cast in steel molds (rapid cooling) and some are sand cast, slower cooling and so the end result would be different.
I'm not a design engineer so I'm not sure why you want to go to class 60.