Brake upgrade

Was looking into a brake upgrade on my 85. It has oe wheels off an 96 vette 17 inch front and 18 inch in rear. did some checking but found that they suggest addapters to put these wheels on my car? it doesnt have any addapters on it ? in order to upgrade the brakes to 13 inch rotors front and 12 inch in rear do I need to put said addapters on it or will the offset on these wheels be ok and not cause clearence problems. any suggestions? or just go for it?