Huw
Try Car Build Solutions
http://www.nfauto.co.uk/cbs_products_new.htm
They do a seriously long accelerator cable that works well in my Dax.
I know Paul Walton used the same in his Tornado
Route the cable with as few bends in as possible (if possible direct from the pedal down the right tunnel (At first I was going to loop around and down left tunnel as the cable was long enough but this adds a further 180 degrees of bend for the cable to work with) - out near the gear change mechanism then past the chassis members and up to the carb??? above the gearbox)
Probably need to manufacture the end brackets but at least you have the bit in the middle!
Ian