Engine swap?

First I would take a really close look at the work involved in doing this and if you really want to do it at all. To keep it simple, you will be swapping out everything from the engine, transmission, transfer case and electronics including making a custom dash to do this swap. Essentially turning the Expedition into a Tahoe or Suburban with Ford badges. That is because almost none of the electronics will be interchangeable and because of the way they are integrated into the vehicle it gets very complex very fast.
Step one is going to be making a list of the options and features you have and what controls them. Now let's say you buy the adapter parts so that you only swap just the engine itself, you need a way for the Ford transmission to talk to the GM engine controls. For that you might be able to use a standalone ECU for the LS, but will that ECU control the Ford transmission? How about the ABS module? Air suspension? Most interior stuff will be controlled by the Ford body control module, but will it work with the GM ECU?
It's one of the reasons why many project cars turn into money pits and still end up with warning lights on and never really finished. So, think about what you want as the end result, and would it actually be better to swap something like a Coyote into it instead. Not saying it cannot be done but you are looking at a lot of engineering to make it work.