One point most folks don't consider is the titling ramifications in the future once the original engine is removed. If you ever intend on selling or even giving the truck away after you change the engine and you happen to live in a state that uses the engine number for the VIN on the title (pre '56) you need to be aware that the number on your title will no longer be on the truck. You can save any future owner a heap of headaches by retitling after the swap is made.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.