Waltham (Mass.) Contributory Retirement System is adding a $7.5 million investment in global fixed income and $5 million in private real estate. The $155 million pension fund is adding the new investments for diversification, and funding will come from a general rebalancing, said Joseph Juppe, board administrator. Searches are under way for managers to run the portfolios; selections are expected in May. Investment consultant Segal Advisors is assisting.