Stuey. You’re right in that some additional horsepower was found by using the springs rather than the solid bushings between the rockers. It would appear that the springs do help to settle down any unwanted movement or bounce of the rockers when they are trying relax between valve spring actions.

The offset of the rockers at some of the valve stems for the Y engines is a necessary nuance when using the stock rocker arms. That offset is required so that the pushrods are all centered within their respective holes while requiring only a single rocker arm design for all valve locations. That’s why the stock rockers have that extra long pad for the valve stem end. It’s important that the pushrods remain centered in the pushrod holes and this makes it difficult to center up the stock rockers on the valve stems using the factory rocker arms.

When using aluminum roller tipped rocker arms, the adjusters are offset in the rockers so that the rockers can be both centered over the valve and the pushrods centered within their holes. This requires three different rocker designs to allow the roller tips to be centered squarely over the valve stems; left offset, right offset, and zero offset for the pushrod adjusters. To complicate the roller rocker arm issue,the iron heads take a different combination of offset rockers versus what’s required for the aluminum heads.