SCOTCH PLAINS — Last month, Rep. Tom Kean, Jr. (R-7th) was in town to present township officials with a ceremonial check for slightly more than $2.7 million that will be used to help finance the new firstresponders headquarters that is planned to be built on Plainfield Avenue as part of the downtown redevelopment efforts. The latest tranche of money will be added to a $1-million state grant announced last October to help finance construction of the new facility that will house the police and fire departments, the rescue squad and the township’s office of emergency management. Moving those departments out of the downtown is a key aspect of the redevelopment plan for the central business district, and township officials have focused on the Plainfield Avenue properties — two side-by-side lots, one, a public-works yard and the other, a grassy and wooded three-acre property — as a suitable site for the past several years. The redevelopment plan, which the township council approved last August, envisions a two-story, 70,000square-foot building extending across the length of the two lots opposite Memorial Field.