I removed the old packages and instead made a script to automaticaly create a backported opera version for trusty.
Here it is:
https://storage.fr1.cloudwatt.com/v1/AUTH_71c6d0f9c3eb4f5a95cebeae99f3b468/Opera_Repackaged/backport_opera_5x_to_trusty.sh
Or here:
https://gist.githubusercontent.com/ygbourhis/2033f03f93377b71c29fa0fcbfd71b75/raw/14fbac7c467891c7d9ce4917b74d9df2bad8a5cb/backport_opera_5x_to_trusty.sh
Once downloaded make it executable:
chmod a+x backport_opera_5x_to_trusty.sh
And simply launch this command in the directory where you downloaded opera:
./backport_opera_5x_to_trusty.sh opera-stable_52.0.2871.64_amd64.deb
(Replace opera-stable_52.0.2871.64_amd64.deb with the newly downloaded version)
You can find the source code here:
https://gist.github.com/ygbourhis/2033f03f93377b71c29fa0fcbfd71b75
Hope this helps.