I've got 3/8 pushrods on my hydraulic flat-tappets, but rollers tend to be taller. I'm not sure 3/8 rods would clear with a hydraulic roller lifter. Mine are extremely close clearance at full lift and require each rocker to be within .010 of center or I get a very slight rub. I had to re-shim after break-in. I noticed a few aluminum scuffs on my rods when putting my inner springs back in. Nothing since then.