I guess the question is which one Nige, there's normally three on most cars. It;s probably one of the rear wheel cables (they catch all the salt and therefore corrode), and wouldn't be that difficult, unless GM have hidden the inner ends somewhere...
Its much easier if you drop the exhausts. Bit fiddly but quite do-able. Remember to check the adjustment on the h'brake shoes first, then the auto cable adjuster does the rest when you crank the handbrake a few times. OCW supplied me all the parts, FYI. Good luck !
