[Rick Parker]

Ron: The Isky adjustable guide plates are a very good and often overlooked idea. They can be carefully tack welded (Tig) after final adjustment and alignment is achieved to eliminate future movement.
Take your time to get the roller directly centered over the valve stem. Recheck after tightening the stud on the guide plates.
Don't be so quick to denigrate the heads you have. They are marketed at a very attractive price point. Yes they may need to be "touched up" but just treat them as castings and add good hardware, pay attention to details and you'll have a very good set. Many that aren't aware of it, have their pushrods and rocker tips misaligned on 289, 302, & 351's. It is very common. That was the purpose of the shaft mounted rockers being developed along with eliminating the side to side flex in the stud as the valve opening forces are exerted upon it. Cycle the engine and look at the areas where the pushrod gets close to the head itself in the slot. Be certain they do not "bottom out" in the slot (doubt they will) unless you are using a high ratio rocker arm (1.7+). Also keep an eye on the area where the spring is under the rocker arm close to the stud sometimes the rocker will hit on the spring retainer.

You're on the right track....just keep an eye on all the details.