Upgrade Certificate Server from 32 to 64 bit
In some older documents Microsoft stated that there was no support for upgrades from 32 to 64 bit:
http://technet.microsoft.com/en-us/library/cc755153(WS.10).aspx
This is no longer the situation and there is support to migrate 32 to 64 bit, the Active Directory Certificate Services Migration Guide covers the steps required:
http://technet.microsoft.com/en-us/library/ee126170(WS.10).aspx
This process went smooth and the previous tech doc was all that was needed.