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

.039 ... WOW !!

Here's one downside to "full time" ... how do you know when you have too much or not enough.?!?! Making adjustments requires pulling the top end and.

In hindsight I wish I hadn't bothered with this mod !!

I do the same mod on the Indy heads with external oiling lines, .039 restrictor to each head with solid roller cams and Harland Sharp roller rocker

I measured my rocker shafts OD at .8725" and the rocker ID at .8765". That gives me. 004" clearance on each rocker. That's much more than I was expecting. Restriction size will be a guessing game for sure.
I seen a thread where member Clanton, used a modified mig welding tip under the rocker shaft. I tried the fit, and it fits really good. The tips will need to be shortened (I think he mentioned 1/2") to fit in front of the rocker shaft stud, but after the stud is put in, the orfice tip cannot come out. This way I can make and try several different sizes, simply by removing the rockers. I'll start with. 060" as an initial size, and go from there. I need a set of Andy's "see through" valve covers! Lol. BTW, I'm using the Mopar 4006452-A aluminum heads.

I would not restrict a non roller rocker.

The only rocker I have ever restricted was needle fulcrums.