It depends in some part to what cylinder head you're using and what size/shape the pushrod hole is. Most, if not all early cast iron heads used these holes as pushrod guides. They fit they pushrods with a small amount of side clearance and kept the pushrod/rocker assembly in line. Later heads used a rocker arm that was self aligning so the pushrod hole was opened up. The problem with the early heads is that the pushrod hole will only allow a limted amount of lift and only a 1.5 ratio rocker arm before the pushrod runs out of room in the other direction. Most people who use the early heads for racing open these holes up and use guide plates along with screw in studs. Look at the pushrod holes. If you go to roller rockers and the pushrod holes are round and/or opened way up then you need guideplates. If the holes haven't been touched then make sure the pushrod doesn't bind at any point during the rotation of the engine.
BSE Racing Engines