Pre-facelift rocker cover screws replacement for bolts.

My rocker cover is slightly leaking, probably original rocker cover gasket on there (it hasn't lasted too bad), though on most of the you- tube instructional videos they undo bolts (coil pack), looks much easier, whereas mine has screws.
I know, as soon as I turn them the heads will mush.
If I could get the screws out, anyone know the dimensions of the rocker cover head threads?
 
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