Oklahoma Teachers Retirement System, Oklahoma City, is expected to narrow a list to four from six finalists by Friday in its search for two additional fixed-income managers, said Bill Puckett, investment officer for the $5.3 billion fund. A final decision is expected at the boards April 28 meeting. Diversification is the reason for the search. The finalists are Back Bay Advisors; BlackRock; Loomis, Sayles; PIMCO; Payden & Rygel; and Western Asset. The chosen managers will split a $500 million mandate funded from rebalancing domestic equity investments, he said. The funds current domestic fixed-income managers are Mellon Bond Associates and Neuberger Berman, which run $900 million and $550 million, respectively. Marquette Associates is assisting.