If you already have the wheels then do this...
Measure the backspacing on it... measure to the lip on the inner edge of the wheel... (you could get some stiff cardboard or something and cut it so that it sits down on the inner lip of that wheel) measure from that to the flat part that the lug holes are in... I am guessing it will be 5-6" depending on the width of the wheel
Once you have your measurement go to the wheel/tire fitment guide at the top of this forum, go to the section for the drop you have, or will have, and see what backspacing is for your wheel size.... then you need an adapter to make up the difference in size, and probably a lug pattern change too...
EX. You may have 17x7 with 5.5" of backspacing... if you need 4" of BS with that wheel size then you need a 1.5" thick adapter.
I hope that helps, I can probably explain it better on AIM or someone else on here may be able to explain it a lot better for you.
Drew