The two front rods should be adjustable, it should be easy to make new ones in a workshop, the manual shows the suggested geometry http://nacra.us/nacra/nacra.pdf?bcsi_scan_4B3822EAEF26C5CF=0&bcsi_scan_filename=nacra.pdf.
Older model had just a straight spreader through the the mast, I'd say yours is the new one withouth the adjustable rods. I don't see a clear need to replace them anyway, I think you don't get negative rake by tensioning, per your drawing it would tension backwards, as the dotted line on your drawing is behing the center of the mast, right? So I'd just care if you feel the sail is not shaped right.