Hi

How about

Take a backup of the whole database
Install 10.2.0.1 CRS on 2 nodes for RAC
Startup the 10.1.0.4 RAC with 10.2.0.1 CRS
Install a New Oracle home for 10.2.0.1
Shutdown the 10.1.0.4 RAC Database
Use DBUA to upgrade the database to 10.2.0.1
Bring up the RAC and check everything
Shutdown the Database and instances
Use RMAN (you can also switch the database to copies etc) or DD the datafile to VXFS filesystem
Recreate the controlfile
restart the database

Note i have not done a upgrade from 10.1 to 10.2 RAC but i guess the key is getting the 10.2.0.1 CRS up and running right others all should be normal steps.

Wundering did you check with oracle support guys on this i am curious

I am curious why you went up the route of conveting to single instance and then back to a clustered instance ?

regards
Hrishy