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When you say sand the bushing surface of powdercoating, you mean the surface inside the carrier correct?
You may find you need to adjust all areas. If you've built up a good layer of powdercoating on the arm and the carrier and where the carrier mounts into the crossbar, they all may need to be addressed.
There's quite a few members who have powdercoated theirs on the board so I'm sure they can weigh in with what they've done. When I install them on the rear, it can be very easy to drop a similar bushing into the control arm. Introduce the shaft and it's a different story.
Same may apply here. put the bushing over the a-arm shaft and it may be difficult to get it in the carrier, probably due to the excess powdercoating on both pieces.
Either way... it's easier to assemble those pieces on the bench and check for tolerences there vs. laying on your back on the ground without much leverage.