Once I had slotted the plastic, I decided it was not going to be robust enough so started looking for a metal bushing I could put around the plastic and also slot, then drill through that to hold the arm. I don't know what this thing is that was in my bushing and spacer drawer, but being steel and almost the right diameter to slide over the connector on the actuator, seemed like it would do nicely. I cut it off at the height I needed it to be so it would match the plastic piece and it's slot.