If you don't fit the new trailing arms you can't align the front,
and you can lift the front with factory torsion bars as long as you don't have bar work, winch etc. New torsion bars are the same thing with higher spring rate for weight.
Don't use shackles unless you want you insurance company to tell you to get stuffed when you hit someone or vise versa.
I am an on seller for Cal offroad which makes a 3" kit for the Navara, which is the same as snakeracing, just better with more options and it costs less, the arms are the same, his just have blue paint, plus you don't have to deal with snakeracing who thinks his gods gift to the suspension industry!
Let me know if you want kit or you can mix and match to get the right set up.