Yes, they can be used if the head is machined for 7/16 screw in studs. Most aftermarket BBC rockers use that size, so verify that's what the rockers are. Several disadvantages though, the Mercruiser valve cover still does not provide adequate clearance for roller rockers and as has been mentioned, the rocker ratio is less on the BBC rockers, so you end up with less valve lift and duration by using them. So in some ways a reduced benefit by using them.