Assuming your code is running in a little-endian OS/Machine (like Windows/Intel), you can just reverse the individual bytes of your packet, for example, include the FMX.Types unit in your uses clause:
type
Tconnecting = record
a: int64;
b: integer;
c: integer;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
Packet, BEPacket: Tconnecting;
begin
packet.a := $0102030405060708;
packet.b := $01020304;
packet.c := $05060708;
//big endian packet
BEPacket := Packet;
ReverseBytes(@BEPacket.a, SizeOf(BePacket.a));
ReverseBytes(@BEPacket.b, SizeOf(BePacket.b));
ReverseBytes(@BEPacket.c, SizeOf(BePacket.c));
Memo1.Lines.Add(Format('a: %16.16x => %16.16x', [Packet.a, BEPacket.a]));
Memo1.Lines.Add(Format('b: %8.8x => %8.8x', [Packet.b, BEPacket.b]));
Memo1.Lines.Add(Format('c: %8.8x => %8.8x', [Packet.c, BEPacket.c]));
end;