If you have the regular Herald or non-rotoflex Vitesse layout, the front pipe is 46" long, the rear pipe 53". This depends on matching the curves and exact layout to the original, so there is room for variation.
The Vitesse Mk2 layout is different, sorry I don't have those figures, but I would assume the front pipe to be very similar in length.
The union sits betweent he front and centre outriggers. It's biased towards the front so the more complicated routing of the front pipe along the bulkhead is more easily achieved. The largely straight rear pipe can be fed through the outriggers more easily,