The slots go on the bottom side of the shaft. The bottom of the shaft is unloaded when the car’s weight is on the wheels.
Adjust the threaded bushings so the shaft rotates easily before welding. They are NOT to be tightened hard into the UCA or the shaft will be in a bind. Torque them and then back off until shaft is centered and will rotate freely. Do not back them out more than 1/2 turn.
Weld the bushings in three places as shown once the adjustment is achieved.
Use 90 degree zerks, aligned parallel to the long sides of the UCA.
If using an o-ring style bushing, be sure the slots extend past the o-rings. This allows grease to leak past, avoiding overgreasing pressure from blowing out the o-ring. The slots allow grease to easily reach the entire threaded area of the bushing.
When completed, the shaft should rotate freely by hand. This avoids having the bushings in a bind which makes the bushing threads wear rapidly.
Money you enjoy wasting is NOT wasted money... unless your wife finds out.