I looked up '63 Impalas on Hagerty.com's evaluation chart. $16,100 in fair condition + 10% for a 4 speed transmission. I would call them way too optimistic for a 4 door hardtop. That is with a 327 w/4 barrel carb. Is the interior all moldy & rotten, or just dirty. Are there rust holes in the floor under the carpets, or anywhere else? Some folks like to try & sell barnfinds just like they found them, but I would try to clean it up first. It might clean up pretty nice with some cleaning products & elbow grease. It definitely is a pretty rare car with a 4 speed in a 4 door hardtop.