Re: 462 Double Hump Heads & studs
Somehow, the rockers have to be held straight and lined-up on the valves.
There are 3 common methods available: the slots in the heads, where the push rods go through, fit tightly to the PRs; guide plates, which do the same thing, but the holes in the heads have to be much larger so as not to interfere; and "self-aligning" rockers, which have little "rails" on the tip that enclose the valve, also requiring the larger holes through the heads.
One AND ONLY ONE of the 3 methods must be in effect at any one time. If 2 of them exist, they will "fight" each other, and almost certainly, something will bind SEVERELY somewhere, and parts will ALMOST CERTAINLY be destroyed brutally.
The slot method was used on virtually all stock SBCs (except for a very few high-perf ones, which used guide plates). The SA method is used on all SBCs from around 87 up. The guide plate method has been the favorite for racing for many years.
IMO the SA mehtod is "best" for a street motor, because it unambiguously forces the actual thing you want to control (rocker tip location on the valve stem) to be right. However it doesn't allow for ideal geometry in all cases when very high lifts are used.
Guide plates is the old standby. Been working well for A LONG TIME.
Slots in the heads has several issues (not least of which is, forcing the casting material to bear directly against a moving part) and is the least preferable IMO.
I would strongly suggest that you take the heads off, have the bosses milled down correctly and the holes for the PRs drilled out, and install guide plates and the studs with the hex. The studs on stock heads go into the water jacket and will leak coolant into the crankcase around the thread if not sealed. It's near impossible to guarantee that the ones without the hex shoulder will stay sealed over the long term, because they don't tighten "against" anything.