I must be blind because I do not see the 64 bit version available for download. I clicked on "clrmamepro download" and ran the .exe which it then installed into my "program files (x86)" indicating it's a 32 bit version.
you've seen this on the wip page...well...it's work in progress, the public can't access it yet. Be a little bit patient, it won't take that long before the version becomes official...