Isn't 143.5 mm about 10 mm longer than the streamline? the celluloid (red version of jade?), clip and cap band suggest a very early streamline using Duofold parts while the nib (replacement?) and section appear to be later Duofold items.
It must be said that just about all British pen makers copied the Duofold for their button fillers. Have you checked the threads against other Parker pens?