When I restore columns and adaptors I always clean the paint/rust off with a wire wheel on my bench grinder. Then I wetsand the parts starting with 220 going down to around 600 until the surfaces are smooth. Then I prime the parts with a good sandable primer and when the primer is dry I sand off the high spots and if needed prime a final time. For paint I like the SEM Trim black. It has a very subtle sheen and light texture to it and looks great for columns and interior parts. In fact I am planning on painting all of the trim including the dash frame in my 72 RR with this paint ans well as all of the plastic trim on the outside of the body.
Do not lose the nuts for the adaptor, they are a special nut and I am not sure if they are reproduced.
Joe