Tim,
Only my opinion, but if this were a 1915 Hooshmaroosh, and the only one available in the world, it is a different animal. But Model A's in every conceivable condition and price are available everywhere.
Whatever this guy is asking is probably what he paid foolishly and then let the car sit, in my mind actually reducing the value.
Whatever you feel it is worth with essentially a broken motor (would you buy a car off the car lot with a broken motor, no matter what they said?) is what it is worth; or whatever he is asking, then take off $5K and walk away. If he is desperate, you'll get the car.
If not, buy another one. You'll be happy you did. This pig has been around the loop apparently and you don't want to be in that routine unless the car is super cheap. Walk away is my two cents. But you are the mechanic in charge.
If you do get it cheap, I bet it runs perfectly after you put a little effort into it.
JackD