dssur
+1y
set the axle at your desired ride height. If you arent sure what you want the ride height to be, usually 3 - 5 inches up is good. Install the lower bars as close to parallel with the ground as possible. If you have to angle them, angle them slightly down, this will help squat the rear axle under acceleration.
Install the upper bars as close to parallel to the lower bars as possible (when looking from the side, from the top they will be triangulated) Dont pinch the front mounting points together, you want them equally spaced in the front mount as it is at the axle. If you do pinch them together it will behave as badly as a two link, with wild pinion changes and a lot of fore aft movement.
Keeping the upper bars a little longer than the lowers is best so that they are similar length to the lowers when the uppers are triangulated and installed, although most shops do the opposite. Avoid having short bars on top, thats how you get pinion angle change.
Ideally you would want the bars as long as the driveshaft (either to the trans on a one piece, or to the carrier on a two piece) to minimize fore aft movement. But I have 28 inch lowers on mine and there is no push or pull on the carrier bearing.
I built my own 4 link, it has 13 inches of lift with 0 pinion change throughout travel and 0 fore aft deflection at the carrier bearing. I tack welded everything up and used a jack to run through travel, at 15 inches liftthe pinion started to droop a little and there was the slightest push forward on the carrier, but even longer bars would fix that. Pics in my profile.
My point though is TEST it out. Its not a job to be done step by step and then finished, tack it all up and try it, watch what happens when you run through the travel and if needed break the tacks and try something else.