@Mike Self and @'76mintgrün'02 Thanks for the help. My VIN is 2584627, so just after the transition. The grills on the car are both 'shallow' (although both are missing the top rail and were painted black).
The car had one of each - SB43 and SB22 - retainer rings, however.
Armed with this knowledge, I will go through the spare parts pile to see if I can put together a matched set, or I might be in the market for some trim parts.