1970 dart swinger big block $7700.00

i bought the car about four months ago to keep it and do some work to it. so the next day after owning the car i put a new exhaust system & new holley carb on it. then bad luck hit and now i need to sell it. i recently had it at a local show and i was talking to someone with the same motor as i have and he pointed out that the heads on the car were four bolt heads therefore they are 413. also the stamp on top has a 4 and then it looks like a faded one after that so it has to be a 413.