Car #1, ex 4 cyl, carbed, you dont know how the motor runs, I say NO to it.
Car #2, looks like a great demo derby car.
Car #3, winner. $6500 is not all that bad for that car with all the stuff on it (I think its a little too much but you might be able to get a deal). It's a race/street car, that you can race today if you want. He said he has receipts, dyno numbers and that leads me to believe that its not just hacked up and put together. That motor can take more than a 100 shot on it. Put another 50 shot on it and you have a low 11 sec car.