Okay, so am ready to tackle this problem. Having never seen a rear plate, with or without the notch, am thinking maybe a 1 inch dowel, cut in half, glued to a plate then making a mold from that. Is that the right size? I can WAG the length, just not sure of the diameter.
That sounds about right (1" dia), but you would want to glue it to the mold, not the plate, to make the indent...
Or am I looking at this wrong? (it wouldn't be the first time...)