I agree.. the roller cam bearings block off the oil passage.. because of the cracks I believe the oil pressure is opening up the cam tunnel allowing the bearings to push out I'm going to drill and tap those passages at the mains and screw in plugs.. I think those that are building these motors now should do probably the same thing. If you are still running a Babbitt bearing and need oiling not sure how how that would work out if the block were to crack