An example of how I used CFF explorer to generate the byte array for sampling and roundtripping an MS-DOS header from a .NET assembly.

gistfile1.n

    public ShouldMatchGivenHeaderBytesWhenWrittenToTargetStream() : void
    {      
      def bytes = array[ // dos header start
				0x4d : byte, 0x5a, 0x90, 0x00, 0x03, 0x00, 0x00,
				0x00, 0x04, 0x00, 0x00, 0x00, 0xff, 0xff,
				0x00, 0x00, 0xb8, 0x00, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				0x00, 0x00, 0x00, 0x00,
				// lfanew
				0x80, 0x00, 0x00, 0x00,
				// dos header end
				0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09,
				0xcd, 0x21, 0xb8, 0x01, 0x4c, 0xcd, 0x21,
				0x54, 0x68, 0x69, 0x73, 0x20, 0x70, 0x72,
				0x6f, 0x67, 0x72, 0x61, 0x6d, 0x20, 0x63,
				0x61, 0x6e, 0x6e, 0x6f, 0x74, 0x20, 0x62,
				0x65, 0x20, 0x72, 0x75, 0x6e, 0x20, 0x69,
				0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20, 0x6d,
				0x6f, 0x64, 0x65, 0x2e, 0x0d, 0x0d, 0x0a,
				0x24, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				0x00];

      def expectedHash = bytes.GetHash();
      
      def writer = DosHeaderWriter();
      def outputStream = MemoryStream();

      def outputBytes = array(bytes.Length) : array[byte];      
      def dosHeader = DosHeader(MemoryStream(bytes));
      writer.Write(dosHeader, outputStream);
      
      _ = outputStream.Read(outputBytes, 0, bytes.Length);
                  
      def actualHash = outputStream.GetHash();
      assert expectedHash equals actualHash otherwiseprint "Invalid DOS header";
    }