I voted to keep both or you'll regret it. These trucks will one day soon be hard to find.
The fact that your asking us whether to sell or not tells me you really don't want to sell. Don't let the money make the decision for you. You know how long money lasts don't you? How will you feel when you've spent all that money and no longer have your beloved truck(s)?
I look at it this way...they are paid for and you obviously care for these trucks. Keep 'em.
BTW, I think that last offer is a joke. You have to build up a 350 and install and then you get $1700? After the cost of rebuilding the engine, how much are you actually getting for the truck itself? Maybe the guy would like new paint too? :p