You can do the block or the heads by drilling and tapping the oil passage for a carb. jet or a set screw that you drill a hole in it. I use Carter jets with a .060 size + or - minus .003 on the motors that oil through the block. Are you oiling the rockers full time? If not don't restrict the oil to rockers The reason being that the stock oiling through the cam only allows oil to the rockers around 15 camshaft degrees at the most, I have not taken the time to measure that so that is a less than a SWAG Remember that the cam goes around only once for every two crankshaft revolutions BTW, I use a lot thinner oil , 5W20 wt. in my motors and more bearing clearances than yours, .003+ on both the rods and mains with no oiling problems so far. I don't like STP either but I do use a zinc additive in all the non roller lifter motors I build. I feel your pain on what happened, I have had it happen more than once,especailly in factory motors. I'm not sure what causes it but I'm almost sure it is NOT the loss of oil supply when oiling the rockers with the stock system