You need to get a great score on the GMAT. Both ISB and IIM A PGPX average around 720 on the GMAT and a 20 point deficit will not help but can still keep you in contention.
Both the schools attract a lot of people with a fairly high number of international workexp (esp the IIM A program). So I would reckon you still need to be fairly articulate in expressing your goals, why ISB/IIM-A, why me essays.
Arun
Founder of CrackVerbal - India's fastest growing GMAT Prepration and MBA Admissions Consulting Company. https://gmat.crackverbal.com