So on PCG wiki i saw this line:

More information 64-bit Upgrade Patch (US / UK / German / French / Spanish / Italian) - Adds additional content, higher frame rates, enhanced textures, longer view distances, and more objects with real-time physics.
http://pcgamingwiki.com/wiki/Far_Cry

And chance to install this on gog.com version? Wanna see such tasty things mentioned above :)

The 64 bit version uses patch 1.31 and 1.32 if I remember correctly, but the latest patch was 1.4 which is 32-bit only, and that's what the GOG version comes with, as it is the latest patch. I don't think you can downgrade the game to 1.31/1.32, but there is always the FCAM mod which puts in some of the 64-bit features, but it does also make other changes to the game so won't give you the vanilla experience (though I think the game is better with FCAM).

As I understand it you can install the 64 bit patch over later versions it just creates a separate executable. There is information on steam forums on how to do it.

As for Far Cry 64 Exclusive Content Patch, try this:

http://farcry.filefront.com/file/FC_64ecu_to_32os_conversion;50861

It is a 64 to 32 bit conversion package that allows graphics enhancements of 64 patch and content pack on 32 bit systems...definitely, give it a try!