im bushing my lifter bores on my 340 because i would like a tighter clearance than .003 and get rid of the chamfers also true up the lifter bores . what size hole should be drilled in the bushing for oiling the lifter. I'm going with either hydraulic rollers or mechanical rollers lifters . if i didn't bush the lifter bores the oil hole would be the oval hole from the factory which is about 3/8 tall by 5/8 wide.