Brass is a lot easier to drill using a pin vise with small bits under .050
The brass set screws I buy are allen head with no holes through them and they are easy to drill by hand with the pin vice using those small bits
On the Harland Sharp BB Mopar needle bearing aluminum rockers single shafts sets I use .039 drill bit size works fine for me for the oil restrictor with the groove #4 cam journal machine the width of the stock oil hole in the cam and around .030 deep