Oh for crying out loud!
A crank? He might as well rebuild the motor that was in the thing. The same goes for the head gaskets as far as I am concerned - if one of them goes it's pretty easy to remove the head w/o removing the engine though.
I would change out the thermostat - by the way - check your Summit or similar catalog - there is a type of thermostat that fails open. That means if it stops working it does not stop water flow.
Ask yourself - what don't you want to do again after you swap motors. My guess is - remove the motor again. So do what you can't do unless the motor is out that doesn't cost a lot of money. Let's assume your replacement engine has at least 70K and you want to "buy some insurance" that it will last another 100K.
You can't replace the oil pump($90) , oil pan gasket ($30) , or rear main seal w/o removing the motor. The rear main seal usually comes with the oil pan gasket set.
It's a pain to replace the water pump ($40) , front seal and any freeze plugs while the engine is still in the truck. There is a type of freeze plug that is bullet proof and "bolts" in - at the very least I'd remove and replace the one just above the oil filter with a bolt in freeze plug. Because of alignment I'd include the cam position sensor if your truck uses one.(That is $200 item at Ford) You might also consider the timing chain and tensioner($70-90) - but, those will usually last 200k w/o problems.
If you can afford them, this is a good time to install headers, replace motor mounts, flush your radiator, change your serpentine belt etc. - but you knew that.
A day or so before you begin this project put a lot of Liquid Wrench penetrating oil on the exhaust bolts. You can get to them from the top and through the wheel wells. While you are there-pull the little rubberish flaps that keep dirt and grit out of the engine compartment off. They are just snapped in - and will snap back in afterwards. It will make reaching a couple of things easier as you start disconnecting things.
That's how I see it.