In six weeks, the Medi-Cal program that provides health insurance to 19-year-old Justin Spring will plunge into a transformation affecting 100,000 low-income people in Ventura County. Leaders of the program are conducting a widening education blitz aimed at letting people know the state-run system for the poor and disabled will become a locally administered plan where patients have to choose a doctor or be assigned to one. Spring, covered by Medi-Cal because he’s blind in his right eye, should receive letters and lists of doctors within days. Radio ads explaining the changes will run on different stations 360 times a week. But on Tuesday afternoon, standing in front of a clinic that serves poor and uninsured patients, Spring summed up his understanding in four words: “I don’t know jack.” On May 12, California Department of Health Care Services officials gave the Gold Coast Health Plan a green light to start covering Ventura County’s Medi-Cal population on July 1 as a managed care organization designed to save tax money and deliver better care.