I don’t think drilling and plugging would be a good choice. From the looks of the pictures you posted, the cam bearings are either fretting or rotating in the block on occasion. The oil may be saving you on that front.
If the oil drillings are .250”... At 100 psi of oil pressure, the exerted force on that square area is under 5 pounds of outward force. Not enough to open that crack in my opinion.

"use it 'till it breaks, replace as needed"