Note: There will be an installer. Do not use it! It was meant for 2011!!!
Instead, open the folder mods/required/Core Data/jar
From inside the jar folder, select all the files and folders and create a zip file with them. Name it whatever you want; this will be your "Jar mod" for MultiMC.
Now, open MultiMC.
Create a new instance of the Beta 1.7.3 version.
Launch this Minecraft instance now. This will download the jar files you will need later. Just open Minecraft, you don't need to play. Once the game is started, close it. With the X on the top right corner (yes, there was no quit button yet )
Now, right-click on the instance icon and select "Edit instance" in the dropdown menu.
From there, in the left side menu, click "Version".
You will see a window with "Minecraft" and "LWJGL" in it. On the right hand side of this window, click on the button "Add jar mod" under the "Advanced" menu.
This is where you select the zip file you created earlier.
Launch the instance once more time and close Minecraft as soon as loaded ... we are not done yet.
Go back in the YogBox folder, find Mods/required/Core Data/resources.
Copy all you see in this folder into your YogBox instance folder from MultiMC. It should be something like: MultiMC/Instances/YogBox/minecraft
You can now launch the game and create a new world.