I'll take door #3, Art, Most scope base screws that are in the #8 size that I've seen are 8-40. Jump just type in what size drill needed for 8-40 thread or tab in google, I bet it will tell you. Off the top of my head it's a 20 something in the numbered drills. Remember my SKS mount came with 8-40 screws and I drilled and tapped it.
Joe