2"? thats not too bad. I'm not sure I would worry about it. Ideally, the eye's would be level, but you don't often reach that. Some stock setups aren't even this way. But what you want to avoid is an obvious slope.

In a front application, one thing this is going to effect is your caster. Another words, if the axle has 8* caster built into it assuming a level spring pad, having the spring slope is going to throw that number off.

-Rob