Sure ... that'll work great ..
You are just using the points as the electrical switch to turn the light on and off.
Thats what points are... a switch.
Thats better than either method suggested in 'the guide'.
Rigging up the batteries and wires isn't necessarily 'easy' though.
If you have an electrical meter .. you alrerady have a continuity tester .. use it instead.
As far as which wire to connect it to .. you will easily figure that out when you come to it.
You may find it easier to unplug the wire going into the coil (from the points) ... then - just run the wires from the 'continuity tester' you've made to both sides of the points.