The Viper body is already very strong. The rollcages sold as a bolt in kit are just "cosmetic" improvements. If I was you, I would take a local rollcage builder to install something strong protecting againt side and front windshield impacts. For $1500 you can have something really customized and nice looking that will provide real protection. Price will easily triple for a 100% FIA certified rollcage.
But again Vipers have a creazy strong survival cage for amateur racers. As long as you stay inside the cockpit you will likely survive a big impact. The ACR has a very good 5 point harness. Use it everyday ...
The better is to drive such a way that you will not be involved in any incident. Put this in your head. This is your best protection.
