1969 Swinger "340" and parts car

The original engine question is certainly a valid one. That will be easy to determine with just a little work. There's a smooth, machined pad on the passenger's side of the block immediately above the oil pan rail "about" half way the length of the block. There's a sequence of stamped numbers there. If it's the original engine, those numbers will be the same as some in the VIN of the car. If not, they won't match. That could certainly help bring top dollar considering the car's condition. Good luck.