I need to upgrade the brakes on my RS, im going for the XR4i rear disc conversion but need some advice on the fronts, currently i have the S1 setup with grooved discs and mintex pads, im undecided whether to fit s2 calipers (do these fit straight on?) or use the cossie setup

Whats the best option? how hard are they to fit? and whats the difference between 2WD cossie calipers and 4WD calipers and would both types be okay to fit oh and will i have to change the master cylinder?

Anyone?