I personally wouldn't worry about buying a Viper that's been tracked. Come on how many haven't been to the track? Heck that's what they were made for. I also wouldn't worry about a new or rebuilt engine done by Arrow. They do top flight work, I have first hand experience with this and would consider it a positive selling point for my car. In fact the new engine has low mileage on it and this is a plus in my view.
However, all of this should have been disclosed. Why the heck wasn't it I ask? This does lead me to believe that the seller is not disclosing something else, a wreck maybe? The seller should have been upfront about the work. After all it is not hard to get the service record from a Dodge dealer so sooner or later it would have come out anyway. This all leads me to question the honesty of the seller. I would like to hear his side as to the 50% he says 85 of 200 was wrong about because even if 85 of 200 was wrong about 50% (which I doubt), the remaining 50% is already too much. If the seller was 50% wrong then he mislead 85 of 200 and should reimburse him for the trip.