72 Duster Resurrection

Yeah the coating has to go in the lower tapered holes. I'd probably carefully use a round or semi round file. There are powder coat dissolvers out there. Never tried them but I think Eastwood may carry it.
You should be able to find a local powder coaster in your area and have the other one done. Or sent it off to Leanna at Phoenix Powder In TN. (She's a member and would NOT coat the holes.) Or clean and paint.
Last time I installed UBJ's I temporarily installed the UCA's in the subframe before carefully threaded them in and tightening with the big socket and a cheater pipe on the breaker bar. If done correctly they are perfectly fine without welding. And, they are somewhat fail safe because if the threads give out the upper arm is still captivated. Chrysler built many millions of cars and they didn't show up on recall lists.
Many have been ruined by auto machine shops who throw them in a hydraulic press and drive them out thereby ruining them. That is a case where spot welding would work to save the parts.