value of a ZL 1 clone with a real ZL1 motor

[L78M22Rag]

I'd be interested in your take on this scenario...
I've been trying to buy a local car off a guy for a looong time. The car is rare (but non-matching), so I've spent years tracking down its original motor in case I eventually get to buy the car - I followed a lot of rumors and went down a LOT of deadend roads. One day... there's a motor for sale in the local paper and (after recognizing the VIN) I buy the motor... its never been decked and all original! I've been straight forward with the owner of the car telling him that I found and bought the car's original motor. I still want to buy his car, but now he wants to buy the motor... and the car continues to sit on a couple of flat tires - as it has for the last twenty years (at least its not outside anymore).

So now what should I do?