From the voice of experience - buy a car from a current ViperDays participant if you want to run ViperDays. Running that series gives you access to the best mechanics and car set up folks around - the ViperDays cars are most definitely the best prepared cars out there. ViperDays participants know the weak points and should be maintaining their cars to the highest standards.
Henry's car was professionally built, but not by Viper people. After we bought it we replaced all the suspension set up, all the ball joints, all the hubs, the front splitter, and went through a TON of other items with help from folks like John Archer. It's a steep learning curve going from ViperDays to the Viper Racing League, but luckily there is a wealth of knowledge there and folks willing to help. it's been a great first year for us - but we couldn't have done it alone.