You have enough of a shot that it's worth applying to H/S/W. As you've already mentioned, your GMAT/GPA will be an issue (although being in engineering, they will cut you more slack, as engineering programs are known to grade on a much harsher curve than arts/sciences or business).
Every top b-school values Peace Corps experience, so I would focus on schools you really want to go to, rather than "which schools I can get into" because any of them will give you a serious look.
At this point, the only thing you can do is to boost that GMAT -- at your current score, you're going to be on the margins anywhere; with a 700+, you should be competitive for any top b-school, including H/S/W.
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