Using a small drill press, the smallest ones, you could turn the base 180 degrees and clamp it to the table . Then drill, then move and so on.

But honestly you can not skip the drilling and tapping. I used a nice pro Makita 2 speed Rotary drill, new drill bits and Big Gator Tap and Drill Guide Block. Plus a clamp or two.

Using the Big Gator Tap and Drill Guide Block when tapping was a big help and i did not break a bit. Quality cordless drill with a machine tap also will help speeding the last part of the process.

I also use transfer punches as above.

Also drilling before mounting the rails against a straight edge ??? The acceptable error is not so much as you imagine it. If you do not do things precisely from the start you will have to open some rail holes further.