Hmm- I haven't tried backporting. But, it sounds like you are doing a full export. Don't do a full export- try doing a export specifying the tables you need or a particular owner (example OWNER=TESTSCHEMA) when you import, the constraints,etc will still come. You just won't get the user pre-created. You must re-create the user first in the 7.3 db and then import. Be careful to set all privileges for that user prior to import.
Kimberly