No factory installation with a 12 inch converter ever used 7/16" bolts. The main difference between the 912 and 248 covers is the bolt pattern, BB 727's used four small bolts while the SB used two. The shape and width of the raised arc area is irrelevant because the converter bolt heads are behind the rear surface of the block as is the rear of the cover. Bolts contacting the cover are because of a crank thrust problem or distortion of the cover.