I will come to Roush’s defense, sort of. Per his sketch that design is useless. If it were a axle in a tube (as in a RWD car) his design would work 2 more bars. A torque arm going front to rear and a panhard bar going sideways would make it work well with an axle in a housing.
The problem lies with the bearing cassettes. In a rear end in a car the housing holds the bearings concentric to and in line with the axles. Thus you need to only constrain the movement of the entire housing. This allows 4 bars (two trailing arms, a torque arm, and a panhard bar) to do the job. Three bars if you using a ladder bar setup. In this [go kart]case you need to locate the bearing cassettes relative to the axle as well as the position of the axle/bearings assembly to the frame. Thus to use this bar setup you’d need at least four bars on each cassette to keep things located and in-line.
If you want to adjust ride height put a jack screw up through the bottom of the frame. Reinforce the frame around where the hole goes through it. Put a cotter pin through the top of the jack bolt so it can’t come out on the track.
Now with your kart up on the stand you loosen the screws that hold the cassette and turn your jack screw up or down. Gravity will hold the axle assy’s against the screw. Adjust height on each side and retighten your lock screws.