Its a bad time to sell a truck, great time to buy a truck, especially a modified truck. For $11K, that seems like a fair price. You could probably get more for your truck, but I don't know how much more, and then you have the time and hassle of selling it.
I think you have made up your mind, but since its obviously something you want to do, have you driven the truck? I am thinking that once you see the truck, crawl around the truck, and drive the truck, you will know whether or not you want to make this deal. Both trucks look to be in great shape, but you get a better feeling when you see something up close.