Hey Detroit, I would start by setting the chassis at ride height then set the motor and transmission where they will be and make sure you have adequate ground clearnce. It's best to clamp or tack weld the peices where you think they will be and see how they work out with all the other components before you do any final welding or permanent installations. If the frame needs to be Z'd, then Z it. If you have never done that before, study a lot first and find the best way to do it.