In Computer status report there is a report called
Client Inventory. That report gives information on the OS not sure if it can be specfic to tell 32 0r 64 bit.
Can you create the report and see if that helps
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/77a68d619e380e5488257612005948ac?OpenDocument
Now coming to avoid confusion on 32 bit and 64 bit for upgrade is concerned , there is no need to worry about. Say you have a group called TEST and you have 32 as well as 64 bit clients in the group
Assign both the package 32 and 64 bit one by one using Auto Upgrade.
In the first attempt all 32 bit will upgrade and it will fail on 64 bit
In the second all 64 bit upgrade and 32 bit would fail