I just came back from the DOAG Conference 2009, the german Oracle user group conference in Nürnberg where I had a speech about RAC PreProduction Testing. I have uploaded the slides and the paper to the papers section. At this time, the presentation is available in german only.

To find out whether the database was initially created as a 32-bit or 64-bit database, you can query:

SQL> select metadata from sys.kopm$ ;

When the output contains:  ‘B023‘ , the database was created as 32-bit whereas ‘B047‘ indicates 64-bit.
BTW: A short introduction to converting a database from Linux x86-32 to Linux x86-64 is available in MetaLink Note 341880.1.