FWIW - I now have Windows 7 build 6801 32 bit and 64 bit installed and activated. IF one were to have 32 bit installed, ran Belarc Advisor, used the key it showed for Windows to install the 64 bit version - one might get it to work...... Don't be surprised if Belarc shows your installed Windows 7 as Windows Vista Ultimate..
32bit and 64bit Product Keys Are Not Brand Specific Nor Are They Bit Specific So You Could Install 32bit version and 64 bit version using the same key... and why use belarc.. just use a much more simple tool like KeyFinder