Sorry for beating a dead horse about tire size

Going to apologize first if this is screwed up. I just signed up and have not figured out how this works yet. I seen a old post by Old Man Mopar about fitting a 275/60/15 under the rear of your Duster. I'm wanting the same set up but have a question about the spacer. From what I have read it looks like a 15x8 with 4.25 BS is the wheel I need. I do want to set the back of the car down on top of the tire but cant find anyone that says the tire clears up top. This is my first Mopar so I'm learning as I go. I called Mancini on the spacer as recommended but they had no idea what I was talking about. Hope this gets to you or someone who can help. Thanks!!
Here is the original post
1/4" spacer 275/60