Does Third perch whack out alignment?
I wouldn't call where the numbers end up "ideal". Each trucks going to be slightly differrent, some might end up being barely in spec regarding caster and camber ( plenty of toe adjustment so that's not a problem) , others might be out. Personally I wouldn't go to the third perch unless I had an aftermarket upper control arm to help correct some numbers.
Crazy as it sounds, going with aftermarket rear springs that lower the rear will actually improve the trucks front caster angle, giving you more leeway for a better alignment when raising the perch. How much I'm not sure but its something I'm going to simulate the next time I'm doing my alingment so I can find out.