[camaraderie]

You want to do a sea trial before you part with all your money. Major things can go wrong in a sea trial that can't be found on the hard...engine problems, auto pilot, instruments etc. You may not want to walk away if any of this is found, but you don't want to be left holding the bag either!
My suggestion would be to write the contract with the balance due after survey but with a "holdback" amount designed to cover major cost issues placed in escrow until the sea trial and closing.

 

[camaraderie]

KM... If you already have the engine worked into the price AND a survey on land...then you're probbly not risking much. My own experience is that when the engine is gone...there is more stuff than just that to deal with so your plan sounds like a good way to go about it.