Here're steps.
1.Backup the site collection by using stsadm.
stsadm -o backup -url http://sp19/sites/publishingportal -filename myBackup.bckSee
2.Create a new web application 81. Then create a new site collection named publishingportal in the new web application 81.
3.Go to the new site collection named publishingportal in the new web application 81, then create variation lables same as which created in the site you backup.
4.Restore your backup and overwrite by using stsadm.
stsadm -o restore -url http://sp19:81/sites/publishingportal -filename myBackuptest.bckSee –overwrite
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