Hi,
The reason that it requires the "The source and target operating systems must be the same." to perform a copy is because the copied SIA on the target Oracle 11 would still remember its $BOBJEDIR directory, including solaris_sparc in its path and also for all other servers, CMS, etc.
Thus, you may proceed the system database copy, but, you'd need to be able to delete the old node and create a new SIA/node via ccm.sh.
Before you remove the old SIA node from the CMS database, you'd need to find out its SI_ID, assuming it is 799, from CMC, then stop the SIA and use sqlplus to delete the existing node.
sqlplus CMS_ID@CMS_DB
sqlplus> select objectid from cms_infoobjects7 where objectid = 799;
sqlplus> delete from cms_infoobjects7 where objectid = 799;
sqlplus> commit;
I believe you can find the detail steps from a SAP BO KB as well.
Hope this helps,
Jin-Chong