What's the backspacing/offset? What Riff was talking about with the 285/70/16 assumes that you're using the stock rim, which is actually only 7" wide. The extra width on your rims means your tire should stick out at least an additional 1/2" (correct my math here everyone if I'm wrong) - but it could be more if the offset is lower than +38 (stock offset).

The tire should fit with some minor trimming of the front cladding, but the shop probably doesn't want to do that, which is why they're telling you they won't fit. You may want to have them mount and balance the tires for you then take them home to install them so that you can do the trimming yourself.