looks like he is only planning on going 3" forward. using the f150 box (unmodified), moves the pitman arm approximately 12" forward if you mount the box in the stock location. That 12" puts it near the front frame horns and near harms way considering steep approach angles.
i am planning on moving my front 4-6" forward, relocating coil buckets, trac bar mount, etc. without mocking stuff in place, it looks like i have two options to keep from getting that huge 12" difference with the pitman arm forward:
1. move the steering box back to bring the Pitman arm back
2. mount the box in the stock location and index the pitman arm so that it faces towards the front passenger tire. i havent thought through this one yet, so i am not sure of all of the implications (i.e. clearance of track bar when turning right, etc)
sorry for the semi-hijack, but just some more considerations...