As mentioned, the Venom is from Hennessey.
The Copperhead was a concept car from more than a few years back....think back around the Prowler days....it had a similar look to the Viper....but...well, it was less....well, everything. Smaller, not as outrageous, not as anything...it was about 7/10ths Viper....other problem...it was a V-6 I believe....see the links below.
http://www.allpar.com/cars/concepts/copperhead.html
http://www.iceposter.com/posters/car..._Concept_1997/
I think after they scrapped the plan to make this, they used the "Copperhead" name for a package on the Viper. It was a paint color (Copper Orange) and an interior upgrade....I don't even think there were any power upgrades.