Wow, this is a complicated one. I wouldn't think they need flow at all lifts. You have a lot of oil going up top. If you modify the lifter I assume it's hard and you might want to grind it instead of milling it. I think this needs to be moved to a higher level. Call Ray Barton 610-693-5700 then press 1 and then press 1 again. Sorry to pass the buck but this engine is complicated.