X11 32-bit Mac OS X 64-bit

In Snow Leopard by default it loaded 32-bit kernel:
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Darwin blah.blah 10.4.0 Darwin Kernel Version 10.4.0: Fri Apr 23 18:28:53 PDT 2010; root:xnu-1504.7.4~1/RELEASE_I386 i386 i386
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That does not prevent to work successfully both 32 and 64-bit applications. It is x never experimented, but I think that everything will work.

Yes

At Snow Leopard because there are no separate editions x32 and x64. Hence X11 there is one and the same.
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PS I'd better put the installation disk.