Might be something we all have to get used to. Substitutions that is.
I would not about the grains, Make sure the IBU, (or HBU) match up. You may have to use more or less of the Chinook.
I haven't looked at Yooper's recipe, so I don't know the specifics.
Brew away, I'm sure the result will please you. There are many Fat Tire Recipes out there. One of them might even have those ingredients in it.