Those cams have a much higher lift than stock. So there is a much higher load on the rocker. As a matter of fact, if you read the cam recommendations, they will also tell you that you should also change the valve springs.
Just for clarification, They will fit and work with the stock head set up, but any speed shop will tell you that you really need to change the rocker studs and add the guide plates.
I cheated. I rebuilt my 66 4-V 289 last winter. Bored .030 over, balanced everything, Rebuilt the 4100 carb, kept everything stock in the engine except the cam. i put the edlebrock performer plus in it. I cheated on my heads since they were the close chamber 289 heads. I had them redone with chevy valves (slightly larger) installed the screw in rocker studs and guide plates my self, and added roller rockers. I also changed exhaust manifolds to hipo type.
It will flata$$ scoot ! With the flow masters and dual exhaust, it sounds sweet. For a 289, I can bark the tires all the way up to 3rd gear.
Again, I had the valve job done but i did my own rocker studs and guide plates, since you can buy push rods in most any length, you dont really need to mill the face down to accomodate the guide plate thickness. | 
