Given the lack of documentation, your second best bet might be to refer to the source code of gazebo_ros's implementation

• https://github.com/ros-simulation/gazebo_ros_pkgs/blob/kinetic-devel/gazebo_plugins/src/gazebo_ros_f3d.cpp
• https://github.com/ros-simulation/gazebo_ros_pkgs/blob/kinetic-devel/gazebo_plugins/src/gazebo_ros_block_laser.cpp

Unfortunately there is no good documentation for the plugins. However, you can find some additional information about the sensors from the sources below.

At sdformat.org you can search for the different sensor and there are some descriptions of the different parameters, unfortunately not for block laser and f3d. Maybe you can use the <vertical> parameter to get the same behavior of having several scan layers.

http://sdformat.org/spec?elem=sensor

I found this information for the block laser on what parameters it takes, but not any description though.

http://docs.ros.org/en/electric/api/gazebo_plugins/html/group__GazeboRosBlockLaser.html