The trophy were somewhere close to 1000kgs, if your starting with a phase one I would imagine 1200kgs is possible, replace the whole exhaust and ditch the collector box, delete air con and all associated pipes, ditch the chairs for something ultra light, ditch the soundproofing, lightweight bonnet & tailgate, coilovers, magnesium wheels.. Should do the job! Would go like stink!
Could delete fog lights, transmission tunnel, headlining and carpets, but wouldn't make much weight saving and would compromise use.