Milling the head doesn't affect any part of the geometry directly, except the pushrod length.
However: the intake valve seat is frequently recessed back into the bowl for clearance if the seat is removed by the cut, or to prevent the valve from striking the piston at TDC.
This makes the stem taller above the head, and would normally require a shim added to the stands by almost exactly the change in valve height (actually slightly less since the valve is at a slight angle). Don't assume the valve height changed by exactly the milled amount, you have to measure it. If the amount is small it can be removed from the stem tip by grinding, although it should be done carefully and re-hardened afterward.
The exhaust valve height isn't affected, so any adjustment made to stand height will make the exhaust stands too tall.
If the cam is stock, no compensation is needed for this.
You don't need to know how much the intake valve moved up, you can just do the geometry with a few trial shims.
If this allows no adjustment on the pushrod they must be replaced (at least the intakes) to give 1-2 adjuster threads exposed when lashed.
The usual geometry means that the rocker's pad contact point begins with the valve closed at the closest position to the shaft, walks across the stem tip as the valve opens, reaches the center at 25% lift, and the farthest point at 50%. It then reverses, and walks back toward the shaft and reaches 75% lift at the stem center, and the same closest point at full lift.
I suggest you make a trial, and give us the results and we can go from there.
