I have to say I can't even begin to imagine the troubles you must have had to get the master looking halfway right. I have smoothed off the cab front "cap" at one end to match the other and get rid of the "threepenny bit" effect that was still there.
Anyone needing to fill or reinforce a resin cast/moulding could do worse than mix superglue with model filler (or DIY filler from your nearest Wigoders will work) into a paste that will stick to your workpiece and set surprisingly hard, allowing you to sand, file or carve off to the desired shape.