I have been chasing getting the roller rockers to align in the center of valve stem. I have adjusted the guideplates several times and can't seem to get them perfectly centered.

What is the critical alignment here?

Adjust the guideplates to center the roller on the valve tip front-to-rear. Unless you cut the guideplates apart, you have to compromise to get the best fit for each pair of valves. (and then you have to assure that the guideplate doesn't move as you tighten the studs down onto it.)

Adjust pushrod length to center the roller on the valve tip left-to-right, or between the intake face and the exhaust face of the head.

I've had to use the Isky adjustable guide plates a couple times before to get the rockers in proper alignment...especially when using aftermarket heads. Two different types are available...one for 5/16" pushrods, one for 3/8". Just weld the two sections together after you get them in the correct position.
You want the rockers located square and over the center of the valve stem to avoid excessive guide wear.

http://static.summitracing.com/global/images/prod/large/isk-200-agp.jpg

How much do the Iskys run?

How much do the Iskys run?
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They are about $50 from Summit plus their "free shipping charge"
Depends on where you buy them :waving: