usually, when they advertise the degrees, it will be +/-. try to get your hands on a quality kit though (ingalls, etc) you wouldn't want something so important to fail on you.

for the rears, u could try the washer method instead of buying a kit. u just have to buy some washers and a longer bolt. i'm not sure on exactly how to do it, but if you run a search i bet you'll find it on here.