Any updates to this thread? This is exactly what I intend to do for my project, narrowing the crown vic front suspension. Given my limited knowledge of bump steer and geometries involved, that the lengths of available rack and pinion units would dictate the amount of narrowing you would do. Seem like you should find the narrower rack first, then narrow the suspension unit to match the inner tie rod join overall width, and then make the frame fit the suspension unit. Here is a pic from Longacre...
It's their statement that "...the inner tie rod end must intersect line 2..." that kind of makes me think the available racks set the first dimension. Line 2 is slanted, which means that you could move the rack vertically and get some adjustment, as the higher the rack, the wider distance there is between line 2 intersect points. Of course at some point you will get into the oil pan.
Let me know how you did it and how it's working please? Updates UPDATES!
Craig