However, I do want to add my 2 cents to the subject of rocker arms. Cast rocker arms break, so my first recommendation is a warning, never use cast rocker arms.
Although very many race motors have run successfully with push rod guided rocker arms I have never liked them. It seems to me to be the wrong way to do it, the cheap, small block Chevy, sloppy, short-cut way to do it. Because so many motors have been built, and are still built, with push rod guided rocker arms, my dislike of them must fall under the category of George's idiosyncrasy. So be it. I have always preferred a rocker arm system that employs a fixed mounting system for locating the rocker arm, and rotates the rocker arm on a shaft. I thought the Jesel and T&D systems were bitchen when they finally came along, but they are admittedly expensive, not everyone's cup of tea.
If you have iron heads and are still using the stamped steel rocker arm system, you need a set of roller rocker arms. The factory stamped steel rockers are junk, and they aren't capable of being used with cams of much more than 0.500" lift. However, you do not need to pull your heads and have them machined for studs & guide plates to install roller rocker arms. I have a pair of excellent solutions for you that do not involve push rod guided rocker arms.
The rocker arm above is sold by Ford Racing Performance Parts, part number M-6564-C351. The rocker is equipped with a pedestal that installs in the slotted mount just like the OEM stamped steel rockers & fulcrums. It is non-adjustable, but can be shimmed to achieve the proper lifter pre-load.
If you must have adjustable valve train, these are the solution for you. They are made by Yella Terra, part number YT6015. They also mount on a pedestal in the OEM slotted mount location, but these include an adjuster for the push rod cup, just like the expensive Jesel or T&D style rocker arms. Very stable, no slop, no push rod rubbing against a guide plate. The Yella Terra rocker arms are more expensive than the average set of rocker arms, but if you factor in the cost of removing & installing the heads, the machine work and a set of guide plates and studs, they are cheaper than going the push rod guided route.
If you are considering purchasing a set of alloy heads for your Cleveland, I'd like to mention that CHI heads can be ordered with slotted pedestals. This option is provided specifically for their customers who prefer the Yella Terra rocker arms.