The amount of scrub, in which the 50% lift does not occur at 90 degrees, is frequently used by OEM to improve the pallet (non roller tip)-to-stem wear properties. Heldt wrote a formula to calculate (some type of) anti-scuff by changing the pivot height, but it's over my head!
How much of the "error" (non 90 degree) you want on the pushrod side will vary somewhat between engines depending on other problems such as the horrible LA 14 degree difference between the 59 degree tappet, pushrod angle and 15 degree stem angle.
I'm working on a geo article now with a single shaft, but valves at different angles, so moving the shaft to improve the intake requires correction back the other way on the exhaust, blah.
The Gen-2 426 has its own problem: the rocker stands (both OEM and many aftermarket) are a single piece, which means any height adjustment (mill or shim) affects both valves simultaneously to the same distance, causing much hair to be pulled out!
You are absolutely correct. Different angles, with a common shaft, causes a lot of grief. The Gen 2 Hemi would need new stands made every time a change is made, to get everything right, hence the hair loss. The higher the stands, the closer the shafts would have to get together. That's why Barton's Hemi rockers are all individually mounted. They are pricey, but allow adjustability for each individual valve.
The poly heads would be even more of a headache, unless the stem heights were all set at the exact spec needed, on both intake and exhaust, to get the single shaft at the correct height for both. Then the rockers would have to be designed with the correct fulcrum length for the finished cylinder head. Change the valve length or tip height, do it all over again. Change the valve lift, do it all over again.....etc. Brace yourself, I think I see a bald spot.
