http://www.1010tires.com/WheelOffsetCalculator.asp
You'll have 2mm more inner clearance, and the wheels will stick out 28mm more.
According to Tire Rack you'll be adding 0.7" of tread width and 0.6" of diameter going from a 255/35/18 rear tire to 275/30/19 tire. I would be concerned with the outside rubbing, but it may work.
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