The ones I have on my truck now only stick out about the width of your thumb.  They were designed for fitting 6" wide steel wheels and don't provide enough coverage for the alloys.  When I got the truck it had the wider flares on it and even though I have the 6" steelies, they still seemed to disappear under those big flares, so I got the right ones and installed them.  I can't find the part numbers now, but search this forum or the BWF for "461 flares" and you'll find part numbers.

These have little threaded studs out the back that are designed to go through holes you (gasp!) drill in the wheel arches.  I think you could grind the studs off and attach them with adhesive though.

-Dave G.