Aren't you swicthing to coilovers? if you are it doesn't matter what rake it has on it now :!: :!:
If it were me,
1. install engine and trans.
2. Jack up car and level it, support it on the rear FRAME to give you room to work.
3. support rear end and remove springs, dont forget to support the pinion.
4. put tires on. raise rear to were you like it.
5. remove tires, centre, level and square up the rear.
6. install drive shaft, support pinion angle at 0-1 degree down,
7. support the assembled ladder bars under the car level or slightly pointed down when in center hole. mark the location of the x-member.
8. cut everything out of the way, tack your x-member in
9. tack brackets to housing and x-member
10. doudle and triple check everything, weld it up!