Stock heads have a "guide hole" that is cylinder shaped, so this should act as a guide plate. Or is the side-to-side tolerance too loose.

 

If they are the self aligning type them you should not need guide plates. It does sound like you will need to elongate the pushrod guide holes. If they are not oval them thats what you will need to do. a rat tail file in a drill works great for this. If they rockers are not self aligning then you will need guide plates

 

if you have SA rockers replace them with SA rockers and you won't need guide plates. if you have non SA rockers you need something to locate them, like guide plates.

 

The guide holes look like this...



So there is enough room north and south for the pushrod to move.

 

If the width of that kind of slot is just barely wider than a push rod (like within .015" or so), then you MUST NOT use self-aligning rockers.

You usually only need to elongate the noles if you are changing to 1.6 ratio rockers, whether roller or not. The increased ratio (the rocker ratio being the ratio of the distance between the stud and the valve, to the distance between the stud and the push rod) moves the push rod closer to the stud, and often the slot isn't long enough to allow the push rod to travel freely in that direction.

 

BTW, these are Crower steel RR, 1.5 ratio, NOT self aligning.