did it come with instructions? My nerfs did, but it shouldn't be hard to figure out even without instructions. There's only so many ways a nerf bar will fit on the quad. Different brands of nerf bars mount up different ways, so unless somebody else has those already it will be difficult to help you. If you got a picture of the nerfs for a raptor 350 instead of a yfz that would help too.
Make sure that the ones you've got are for a YFM350.
I doubt they mount the same as the YFZ ones. When I first got my DGs, they sent me ones for a 660...lol...that was a JOKE! Not even close to working! I figured it out and sent them back. The ones made for the 350 fit easily, but don't install even close to how the 660's do.