Hey, folks. I just upgraded to 64-bit for the first time. (Was perfectly happy with my supposedly obsolete 32-bit XP system...until the Great Crash of 2012.)  Installed X2 64bit on Windows 7. (And the X2a update.)  Installed both the 32 and 64 bit versions of Alchemy into separate directories as specified by Camel Audio. The 64 bit version doesn't appear in the plug-in manager.
  As a side note, the 32 bit version, which had worked beautifully on my old system, crackled badly on the new one until I set it to BitBridge 1.

Why bother with getting the 32bit version running in 64bit SONAR? Find the 64bit Alchemy dll, add it to the VST scan path and remove the 32bit version from the scan path. Either alter the scan path by modifying the directories scanned by the Plug-in manager or physically relocate the dlls.

You'll find that Sonar 64bit will run much smoother using 64bit plugs whether they're VSTs or VSTis.

I'm guessing you had a reason to install the 32 bit version of Alchemy (different daw?) but I dealt with this problem when I installed 64 bit (only) Omnisphere in X2.  It didn't happen with 8.5 or X1.
 
Make sure you've got every folder associated with Alchemy being scanned by the plugin manager and then rescan existing plugins, the regular scan all plugins didn't work for me and it bothered me for a few days.