Cambridge (Mass.) Retirement System is searching for a venture capital manager to invest $6.5 million for the $386 million system, said Kevin Leonard, the Segal Advisors consultant who is assisting. Proposals are due July 29. The funding source is still undetermined. Meanwhile, the system has picked Freedom Capital to run a $30 million domestic large-cap portfolio, rotating between growth and value styles. Money for the new fund will come from cutting back Freedoms other portfolios, since it manages about 23% of the systems total assets in domestic value stocks, Mr. Leonard said.