RE: BRIO Construction by the numbers
Attached is a scanned picture of the actual gear plate. You will see the three holes clearly.
Now, how to measure them? just put a small nail down through the holes and then mark the location of the screws. The holes are big enough where if you are off just a bit there will be enough room to position the gear.
To make your job easier, I'll scan a template that you can use to get it right the first time.
Don