You will need a K member, and depending on which transmission you plan to use, you will have to provide a shifter location.
You will also need to get a delete kit for the power brake booster or put the late model hydo system in to clear the left valve cover.
You will need a PCM/engine computer and wiring harness for the engine and some wiring diagrams to make the right connections to the electrical system.You may also choose one of the aftermarket engine management systems such as FAST or Speed Pro as an alternative to the factory EECV system.
You will need the appropriate H-pipe depending on the headers or manifolds you use.
You will have to modify the power steering lines or go to a manual rack.
You will also need an electric fan setup and big radiator to handle cooling.
The oil pressure sending unit from the T-Bird will need to be used to operate the factory guage.
In a 1990 issue of Super Ford, they put a hydro boost system adapted from a Lincoln continental on a LX 5.0. That might work for you as well.
I did a 90LX myself back in the day, and it uses all stock ford parts... another friend did it on his 88 GT as well. Feels a bit weird at first.. but the brakes work great.. and offer the clearance you will need.