A Massachusetts developer has presented a plan to the Board of Selectmen to develop affordable housing at the Pine Valley Mill. A representative of Dakota Partners of Waltham proposed the conversion of the upper floors of the 19th-century complex near the Wilton border into 50 apartments for those with incomes in the $32,000 to $50,000  range. The $11 million project would be funded through a variety of private and government sources, including a $385,000 Community Development Block Grant the town has requested.