Backspacing/Offset question

[Stu2695]

I own a 2008 GMC Sierra SLE 2wd. I've installed a Rough Country front end leveling kit. I've got 17in wheels and have recently purchased Toyo Open Country a/tII (285-70-17). I want to buy after market wheels but don't understand how to figure out or where to go to look for information concerning offset and back spacing. I want to avoid having too trim anything w/ installing the new wheels. Can anyone help or point me in the direction to figure this out.