You still need to bring those wheels way out. I would put those on the front and measure to see how much clearance you still have in the rear.
Looks like you have at least 10mm to go still.
What is the width and offset of your wheels?
Do you plan on rolling your fenders?
I will try and snap some photos of my wheels/fenders. I run a 20" with a 275 in the back.
Measuring offset is not super easy, buy my guess is the wheels will be stamped with it somewhere on the back, either on the spokes or on the hub. look for the width stamped on there and the offset will either read "+20 or it might say et20". I'm not sure if thats the number, just for example.
Then once you have offset and width you can calculate your new offset by adding the spacer
And they aren't 11" wide, my guess is they aren't 10.5". Tough to say, but based on how they look my guess would be a 10" wheel.