Here is my thought on the moldings. Using fine line tape, extend the bottom trim line to the point you want to intersect with the curved vertical trim. Then again using layers of tape, one against the other, following against the curved vertical trim until you get to the intersect point. This way, there are no cuts to be made, the same curve is still there, then you can use a few thin strips of styrene bent to proper shape against each other. Or, you can trace the taped out shape on to a piece of sheet styrene of the same thickness and glue that down to body. Then just shave away the unwanted old trim areas.
One thing, as you extend the trim, it will get to be too fat, as it keeps getting wider as it goes rearward. You will have to shave it to keep in proper order.