I take a different approach when it comes to old cars than what has been mentioned here. It depends on the purpose of the car. Are you going to show it or drive it? Do you think of it as an investment, or nice day transportation? Not every old car is a classic or should be. If you are going to drive it, I think the transplanted engine is an advantage. The sixes were slow, less reliable and expensive to fix. The four is slow, yes, but simple. 5K is a lot of money for the car, but if it's in really good condition and you want to drive it, maybe you could get it for a little less by negotiation.