[Alan Roehrich]

Jim,
Each one of those rockers will likely want a slightly different pushrod length to get the geometry as close to perfect as possible. The right length pushrod for a Crane may not be the same length as the right length pushrod for a Harland Sharp, or a Comp, or a stamped steel. They could require 0.050" or so difference in length. That much difference in length will give a different valve lift. That's how we get the lift correct on a Stock Eliminator engine, by changing pushrod length.

Just checking the pattern across the valve tip will not verify absolute correct geometry. That used to be how people did it, but not any more. The correct pushrod length for a particular combination of parts will almost always yield maximum rocker ratio and lift, and have the least "lost motion". If you change one piece of the combination, the rocker, the lifter, the valve, or the base circle on the cam, the pushrod required to get the best geometry and the most lift will almost certainly change.

There will be slight deflection in a stamped rocker at 330 pounds of pressure, but it will not add up to 0.020" worth of valve lift.

By the way, I will not build a big block any more without 7/16" x 0.125" wall pushrods. I now keep several lengths of each pushrod in order to be able to check my geometry with the valvespring installed, rather than checking springs. I have 8.200" to 8.400" intake pushrods, and 9.250" to 9.450" pushrods, just for that purpose, in 0.050" increments.

Aluminum heads will only be a problem if the rocker studs are wrong, if they are too short (on the 7/16"-14 end that screws in the head), the stud bosses will flex and break. Most commonly on the exhaust.