For migration of databases to be hasslefree without the need to recreate all the nitty gritty stuff like indexes, constraints, etc, my personal opinion would be to use the exp/imp utilities for Oracle 9i. Based on my experience with a couple of P690 machines running AIX 5.2, a 25 GB dump file could easily take me 4 hrs just to import (even with a LARGE POOL size specified). Given the sheer size of your databases, I think the dump files would be exceedingly large as well resulting in the import probably taking a couple of days to complete.
I do have newer machines with VIO architecture in place running AIX 6.1 with Oracle 9i but the import of the same 25 GB dump file was only slightly faster. For your info.