The short block is the engine minus the heads and manifolds. When they say 1969 short block it means the engine is a 1969 not a 1970. If this car is a six pack it would have come from the factory with a special engine which is no longer with the car. This will lower the value perhaps 10 to 15 percent (my opinion). You should ask the seller if they have the original engine from the car and a clear title.