Most of the good older Holleys had two holes per channel, each around .026 to .028"
If you're doing three, then they need to be smaller.
I have two pin vises, or maybe three I forget.
One for hand held and the other for holding in a jacobs chuck.
I assume you are drilling brass screws? (as opposed to some sort of plug inthe blocks).
For the set screws I put the set screw in the chuck of a drill I can run real slow. The drill bit (in the pin vise) is in my hand.
I usually bring the bit in on the hex end.
All of the traditionally trained machineists and techs I've known use nose grease (yea. snot). Being a kid with a degree (a degree of what I dunno) I've experimented with WD40 and such. LOL. When the tip of the bit starts cutting you'll know it. Yup not too much pressure, it won't cut when bent. LOL
I'll see if I have any photos.