You got all the requirements to craft an infernal machine, I suppose you are talking about the lvl 60 one
In fact, we are still able to craft the "old" infernal machine. As long as you are lvl 60 and under, the key wardens will drop the keys for the old, pre-patch-2.0 machine. for lvl 61 to 69, there is no way you can have any drops for hellfire rings events. When you reach lvl 70 you will have the key wardens drop the new parts for the new event released in patch 2.0.
I was needed to clarify this before answering your original question. So now..
So, can I use the infernal machine in all difficulties, or it depends where I get the parts?
In no way you are restricted to craft or use your machine in any difficulty. However, both Keys and Organs now only drop in Torment I or above at the following rates:
- Torment I: 25%
- Torment II: 28%
- Torment III: 33%
- Torment IV: 38%
- Torment V: 43%
- Torment VI: 50%
Here is my source (blue post).