Thanks for the reply. No other numbers embossed on the plastic. I did drill down on all the assembly drawings on an OEM site, but parts shown are visually simplistic and don't show a lot of detail. The rectangular hollow feature suggest it might interface to the frame. Not sure.
Based on how clean it is, and the foam gasket taped to the side, I think it is from somewhere at the top of the engine bay. Perhaps near the battery or the other side near the brake booster. It is possible that it might be from under the dash as well.