I used VHT high temp paint on the pipe to freshen up the look and the stuff is great. I cured it for 1 hour by running the engine once installed. It creates a tough coating much like powder coat that won t burn off.
For a union i used a 3' diameter pipe about 5 inches long with 2 3" clamps to secure the two pipes together.
I lined the inside with muffler cement to make a good seal. I used the original hanger repainted with a new bolt and washers.