They have already done that with their level 1 car. The Level 1 car being all stock suspension and mounting points maintained, but with premium parts and engineering analysis to optimize all the pieces. So there are three comparison points;
Stock, original, or restored to original. (XV's original TA)
Modified OEM using premium parts in a stock appearing package. (XV Level 1 car- red cuda)
No holds bar, unlimited , open class, make it the best it can be within the platform. (XV Level 2-orange Challenger)
Now, can you build a stock suspensded car that will outperform the Level 1 and handle on par with the Level 2? Sure, but you are getting into race car territory and ride quality will suffer at that point. The level 1 system is designed for the best road holding ability combined with ride comfort for an overall improvement that will put a 30 year old car on the same road handling capability as any late model vehicle. For the average guy, this is a huge advantage because all the suspension voodoo has been dialed in for you already an dyou just need to bolt it together. The price is also not much beyond what it would cost you to do all the same pieces individually.
Level 2 set ups are designed for the check book buyer who has plenty of disposable income and wants a classic mopar super car that can do more than trip the lights of the 1320. John can correct me if I'm off base here, but the Level 2 car is not targeting the "average" mopar enthusiast but is after the same market where you see Lingenfelter Camaros, Shelby Mustangs, and Hennessy Vipers. However, if you have the desire, XV will sell you all the parts to perform the work yourself, which is a distinct difference between XV and other builders mentioned.