When ever you do anything to a TTB front end that changes ride height, you're going to need to at least adjust camber and toe (although caster also changes, but it's not a tire wearing angle).
The issue with spacers on a TTB truck arise when the spacers are too big, which make the camber adjustment impossible to get back in spec (camber will be way positive - this can only be adjusted with pivot drop brackets for the individual beams)
On my ranger, I've got roughly a 3/4" spacer under the coils, and it's alignable, but then again I've got a lift on it as well that's been tweaked with...I've heard of people putting up to 1 1/4" spacer on and still being able to align it....you'd have to check on a f150 site to see how thick those spacers are
Whether or not the spacer is too big depends on the truck. For example, a single cab short bed 4 banger ranger will need a smaller spacer than an extended cab 4.0 v6 ranger to stay with in the "alignable" area. This is because a spacer of equal height will have a greater effect on a lighter vehicle (the rangers have the same rate coils across the board, I'd assume f-150's are the same way....if they had different rate coils for different configurations, this wouldn't hold true).