No worries, it'll look hard at the beginning, but just follow the route of the original cable and all will reveal itself.
ONly hard part might be locating the point where the cable enters through the bulkhead into the footwell as it more accesable from the OS wheel arch.
Remove the bungs which hold on the bulkhead lining behind ex manifold, peel back a bit and you can access all behind there......use long sleeves or a long protective glove...lots of glass fibre and scratches = itchy all day.