Selling a car but wanting to keep the engine

I am thinking of selling the 70 340 4-speed Dart in my avatar before winter gets here but I would really like to keep the engine that is in it for my Duster. The 340 is not numbers matching to the Dart so I wouldn't be separating a numbers matching engine from it. I would put the engine from the Duster into the Dart but it is just a 318 and so far I have not had any luck finding another running 340 to put in the Dart. So my question is, has anyone here ever sold a nice, running car with the stipulation that you were selling it minus the engine?
I have a 70 short block.