You have two choices for laser enabled grbl versions (three if you want to use the older Jtech version).
I modified Inventables 1.0c to be laser enabled and you can get it here.
The other option is the latest official grbl release 1.1f which is available in the Inventables download area.
Most of the people that use my version do so because my version does not change the way any of the G-code operations are performed and because it can run at a higher feed rate than 1.1f which becomes an issue with higher powered lasers (> 4 watts).
Some prefer the “official” release but it has some “safety features” built in which modifies how some of the G-code commands work when using the laser mode. Several of the GUI senders have been modified to work well with 1.1f.
Some people have issues with the way that 1.1f handles the laser.
Either solution will work on the Arduino/gShield and the X-controller using the PWM feature.