Thank you guys, some really great comments from you all. Some thoughts:
I just finished watching the Tubalcain videos, which were Machine Shop Tips #55, 56 & 57 (#57 was actually an addendum to #56). I thought they were pretty interesting, and for me they were enlightening. They pointed out to me some things to consider...
1. How I used to accurately locate & drill holes actually had some good points but I now think could be improved. I had a nice little benchtop milling machine from Little Machine Shop with an R8 spindle, and I used a centering microscope to position the quill dead-nuts over the spot I needed to drill. Unfortunately I had to sell the milling machine because the wife & I just moved across country, and I didn't want to lug it around. It was the centering microscope that allowed me to see the spot with perfect clarity. But marking off the initial placement for the holes was always my weak link - possibly getting the right tools would help (starting with a new milling machine!).
2. Tools I have: I already have a nice granite surface plate. Also have jobber-length fractional drills, mechanic-length (stubby) fractional drills, A - Z drills (jobber length) and numbered drills (jobber length), hole punches, layout fluid, combination drill/countersinks, and some layout fluid. ALL OF MY DRILLS are 135-degree split point geometry. I have to quit using the drill/countersinks for initial hole locating.
3. Tools I DON'T have: a height gauge, an angle plate, prick punches, the optical center punch (seems pretty cool, probably not as good as a centering microscope but might do the trick until I can replace my milling machine), and 140-degree spotting drills.
4. Of course... learning how to use the tools I don't have yet.