The way I have mine is:
Power wire from the battery through the battery cutoff switch to the power distribution box. Reused the stock power wire from the distribution box to the starter. Unhook the stock alternator wiring and ran a 6 gauge wire from the alternator to the battery cutoff switch.
Works just fine and the car shuts off when you hit the switch. Just be sure you run good grounds.
I meant to say "just as easy". You only have one wire to deal with on the switch, not two. Guess it really depends on where you mount your switch. I was going to mount a switch with the pull out rod through the back taillight. As I didn't want the switch permanently on the back of a street car. On that side of my battery box I can either switch the one ground wire, or the two wires on the positive side.
It would end up with the same result. For me it was better to use the power wire on the cutoff switch. I have my main power wire for my fuse panel and the alternator wire on the switch as well so it is very convient that way. My switch is like you want to do yours, except mine is under the taillight.
That diagram works fine. The only difference is that our solenoids are on our starters. So run it to the solenoid on the starter and then run a power wire from there to the power distribution block. I actually just reused my factory batter cable to run back to the power distribution block.