I agree with AHY on this, use either a set of ductile iron or aluminum caps and a good set of studs for builds above 600 HP I like and use the Mopar brand of ductile iron caps, I'm not sure if you can still get them or not I am a member of the 500, 600, 700, 800 and 900+ HP HP pump gas club All using Mopar Ductile iron caps Stay away from drilling or machining holes through the side of the block to use side bolts Look at that very closely and then about it If you want a block with four bolt mains buy a new one