First and foremost, your model file should be named similarly to your unlocalized name (e.g., "my_block.json", if you are following the MrCrayfish tutorials.
Secondly, the file within the package "assets.<modid>.models.block" with a .json extension (your model's exported .json file) can be edited directly to contain the line:
"parent": "block/orientable"
OR the line:
"parent": "block/orientable_vertical"
The top one allows for the four cardinal directions, while "block/orientable_vertical" is used primarily when the player places the block below his or her feet.
If you set up with gradlew correctly, you should be able to view the orientable.json file directly within Referenced Libraries->forgeSrc-1.8-##.##.#.####->assets->minecraft->models->block->orientable.json to see the original parent and what it contains.