If you wanna go mad.. strip the entire shell and get some extra welds (i believe its called seem welding/spot welding) for more rigidity/stiffness, then you may want to consider a full set of Bushes, all the braces you can (both upper and lower) a decent set of adjustable ARB's and a cage and your nearly there. Oh and dont forget the tyres as they are very important too. You may want to strip everything and watch the weight also so you can carry more speed through and out of the corners. Then i guess its onto the next thing. brakes and power.