I've never heard that the Union clover leaf logo was for Schwinn? Wonder why if they needed a special logo why not an "S"? Union had the clover leaf logo, and also the "U" logo. They would have been 14/15 double butted spokes. 14ga on each end, then swedged down to 15ga in the middle. They would have been chrome plated originally.
DT or Wheelsmith stainless is what we used to build "pro wheels" in our shop. We used Union for normal everyday wheels. The only Union Chromed spokes we used was the .080/.092 Paramount Tandem heavy-duty spokes. They were good quality spokes, but somewhat limited because they only came in one length. Your spoke length would be dependent on the rim style (700C clinchers/700C sew ups), the type spoke holes in the rim's ferrules/washers, high flange or possibly low flange hubs if not original, and obviously the 3X or 4X spoke cross. Many variables.
You need to measure the rim spoke diameter, the hub diameter, number of spoke holes, enter your desired spoke cross, and enter your numbers into a spoke length calculator. I would not use the original spoke lengths.