? Valvetrain Geometry ?

This is just my opinion, so all please feel free to correct or ignore any of this.

I am not sure a shim here will help the max lift without hurting 1/2 lift more. You just need to check to make sure you don't go off the reservation (valve tip) at any point in the travel.

The geometry on these rockers is not obvious but this is how I understand it. The arm is longest on the valve (closest to the exhaust side of the head) when the arm-to-shaft angle reaches 90deg relative to the valve tip. Movement either way from this point pulls the tip back toward the intake side. So valve stem height relative to the rocker arm shaft height create the angles that determine how the arm will operate throughout its arc of travel and rocker shaft mount placement and rocker ratio determines the m ax arc of travel.

If your shaft-to-rocker-to-valve angles are already at or near 90deg with no lift, then shims will move the starting placement of the tip further toward exhasut side, but pull it back throughout travel (this is not usually the case with SB performance heads). If the angles are < 90deg at the start and will sweep through 90 during lift, the rocker tip will move toward the exhaust side, then back toward the intake side (more common). The trick in my mind, is a balanced travel on the valve tip but favoring for the best centered position of the tip at max spring pressure. It "seems" like this would be easier on guides and valve deflection.

In this case, if you could lift the shafts straight up in line with the valve then yes it would help max lift. But the angle that the stands are machined at is not 180deg relative to the valve stem, so when you shim the mount point you can also move the rocker further toward the exhaust side. This can result in a net gain of nothing (if you are already past the 90deg angle to the valve tip) because even though the rocker rotates further to cover the shim distance the shim moved the initial placement further toward exhaust so the actual position does not change much it at all. Shims can also affect push rod length. Lash caps effectively make the valves longer and will move the initial contact point of the rocker higher (which can also affect push rod height some) and may or may nor help you depending on the angles involved.

Unfortunatley this is all unique with each head/valve/rocker combo and must be carefully sorted out. If we all had nascar budgets to move our valves or rockers up and down as needed it would be easier. I am usually stuck using the parts I have and making do with the result.

I would be interested to see what you end up with here and of course good luck!