Quoted from Zitt:I found the serial cable update to be the easiest. It doesn't really require special hardware... I had a Null serial cable in my cable box.
That said; I understand why PUB cards are considered easier because you don't have to setup a WinXP box.
the updater can run on 64 bit systems it's just the installer that needs the workaround
https://reactos.org/forum/viewtopic.php?t=10988
https://www.vogons.org/viewtopic.php?t=42464