Actuate the rocker through it's lift cycle. With a shoe type stock rocker, you'll notice the contact point 'rolls' across the tip to the outside of the stem. *pet peeve warning ahead:*.... IGNORE ALL THAT CRAP ABOUT "make sure the contact patch is centered on the stem", IT IS 100% USELESS, BS, AND WILL MOST LIKELY CAUSE YOU TO HAVE INCORRECT GEOMETRY!
The correct way to 'set' valvetrain geometry is to put the valve at 1/2 of it's intended lift then set the rocker height so that's the valve stem centerline is square with an imaginary centerline through the shaft and contact point (on roller rockers, it's the shaft center to the roller center. 1/2 the roller counts as valve stem).
This is what it looks like when the shaft location is too low....
When the shaft height is right relative to the valve tip, the pushrod should also be square with an imaginary line from the shaft to the centerline of the pivot ball.... Now for the bad part.... it won't be. Jim Miller holds the patent on correctly built rockers and he doesn't make them for our Buicks. (and from talking to him, they never will be)
"A" is what you shoot for, not "B"
One way to figure out the correct shaft height is to see how far the pushrods are out of square, then average the two. (on my engine, I lowered the shaft height 050"). That will get close with the parts at hand. Once the rocker height is correctly located relative to tip height, THEN you measure pushrod length. (then check everything for square, try and figure out what you did wrong, then do it again. LOL. Doing this right is defiantly a 'feel thing')
Also, DO NOT use standard shaft shims if you need to raise it. They will decrease the ID of the shaft saddle and lead to split pedestals on the head. Not good.
With a shoe type stock rocker, look how the shoe is acting on the tip, if there's any binding, what type of crap it'll take to get 'right', check for binding, then make a decision.
By using stock rockers, the ratio will actually go up as the rocker goes through it's rotation. What you don't want with big lift cams if to have the rocker tip 'wiping' across the tip instead of pushing down on it.
At the end of it all, if you can't make it 'perfect', you can still get a hellova lot closer than just bolting parts together.
Moral of the story, there's a lot more to setting up geometry than measuring pushrods.
