I have not seen with a search any thing like this. I have a 2008 F350 withy the 6.4 diesel. All good so far. It has been a good product thus far to me. However the internet is awash with disaster stories about this engine. If it came to the point of doing an engine rebuild --How compatible would it be to mount up a earlier 6 litre or a newer 6.7 liter into the existing driveline. Money is money but there are a lot more service parts and such for the newer and older motors rather than the 6.4 that was only in use for three years .

 

Welcome to the site..

How many miles on the clock?

People normally post when there's trouble, but many like my 05 6.0 ran with no issues (other than a turbo de-carbon) to the day it was sold for new at 174K miles.
That said,, knowing the potential possibilities, I sold mine to upgrade before any events.. Thought about just repowering it when it came time, but decided a replacement truck was a better path for longevity and reliability.
Huge task to do a backward/forward conversion.

A low mileage used 6.4 would be the lowest cost, or a reman long block a step up and less risk with more warranty.
My 6.0 had trans issues a few months before the sell off, and a low mileage/warranty used was sourced and I installed it. The labor was free of course, and the trans was about a 3rd of the costs of a reman,,

 

This is my first diesel truck. I was always under the impression they were good for 2xplus the expectations of a gas engine. My gas engines have never died on me before I had frame or body issues. I have had 2-300,000 miles on all my gas motors. This truck now has 160,000 miles on it and is running excellent so far. They only used them for three years and that was why I was curious if they could be swapped over to a different engine when the time came for replacement. No anxiety issues thus far. I am very diligent about oil and filter changes. Maybe that is the big issue for people having major problems.

 

I believe you hit the nail on the head, good quality maintenance pays off !
There are a lot of similarities between a 6.4 and a 6.7, but no such thing as plug and play !
I second the info Hayapower gave you , best option.