Actually adding 2" spacers to lifted springs isn't recommend, it can cause coil bind that can damage the springs. It makes sense, I've never seen a 4" lift sold by any mfgr that had 2" springs combined with 2" spacers... If you want to lift it 4"s the right way, either buy a 4" kit or do a 3" with a 1.25" body lift/ motor mount lift. Other areas to address to do a 4" suspension only lift the right way that aren't always included in kits are... IMO: adjustable front trac bar, rear trac bar bracket (or an adjustable bar), adjustable upper rear control arms to correct the pinion angle, longer front and rear lower control arms( they are usually include in kits), longer shocks (as stated above), SYE and CV driveshaft, extended swaybar links front and rear.
You may get lucky and avoid vibes with a t-case drop but you'll lose ground clearance, so what's the point. I think that's about it, I hope I didn't leave out anything.