285/40/18 Tires

I am working on a 94 RMW that I inherited from my dad. Its bone stock with the exception of a set of ION 15 inch wheels. I wanted to run a set up that I saw on the inter web as a guy built a Road Master sedan "GS" that had 18x8.5 wheels and 285/40/18 tires on all 4 corners. Any idea if this set up is a easy bolt on? I assume he has +6 mm offset on the wheels.