To do it right the heads have to come off and get reworked.
Milling down the stud bosses to the correct height would be the first step in order to allow the use of either Comp Cams or Isky small block Chevy adjustable guide plates. Next some new screw in studs with the bottom hex that retain the guide plates are needed.
The old worn guide slots in the heads will need to be drilled out and eliminated so they don’t fight or interfere with the new guide plates in aligning the pushrods.
If you try to cut corners and just put stamped stock rockers or any others for that matter on it you’ll be dealing with issues caused by the worn guide slots which will eventually end up with a failure of some sort.
Since your heads are desirable 093 high compression GTO and big Pontiac performance heads they’re worth spending some money on in my opinion. Or you could sell them and buy some small chamber heads to maintain the compression on your 326 but I doubt you’d be saving any money in that pursuit.
On my own ‘64 421 HO heads I didn’t use guide plates with my screw in studs and roller rockers because the original guide slots machined in the heads were pristine, of course if the slots were worn I would have opted for the guide plates.
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1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
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