State health department officials are putting together a "health benefit exchange" that in less than four months is to offer New Yorkers a marketplace to buy lower-cost health insurance as part of the federal Affordable Care Act. While officials are confident they will meet the Oct. 1 deadline for enrollment to get under way, advocates and others supportive of the state's efforts are anxious. "They are working long hours and there are a lot of complexities outside of their control," said Gwen O'Shea, president of the Health & Welfare Council of Long Island. "Some pieces of the ACA have clarity and some don't. I don't know how you take that complex framework and overlay it on to New York, which already has a broken system."