Well the bore' s are a rough bore, I got the 3.99 and opened mine up, if you run a hydraulic lifter you might be okay, the cost isn't all that much to get them bushed and it's just extra insurance. The lifter galley is raised slightly from the center of the lifter. The cam bearing area can be opened to regular cam and bearings, I went roller and 50mm. It's well worth it for these blocks.