Not to be a sarcastic pr!ck, but you need to clearance the part of the head that hits the pushrod. Different rockers, lifter type can all affect where the clearance issues will spring up. My favorite method is to use some blue dykem on the head, install it with a gasket and a few bolts, install the lifters, pushrods and rockers and roll the engine over a few times. This will usually leave a shiny spot on the head where you need to address things. If the interference is bad enough you won't even be able to get the rocker to seat on the pushrod, and if you try to force it, expect a bent pushrod.
Hope it all works out well for you.