its not advisable to skim your disc, and since you have already skimmed them its not unusual that your brake are not efficient due to the lack of mass required to decipate the heat generated by the brakepads. so even though you have change them to ferodo pads or even any other, its just a waste as the disc could not cope with the added heat from friction generated by these performance pads. anyway, how are the conditions of your rearbrakes? have you check them recently? an inbalanced brake setup will greatly increase the braking distance of any car.
you should first of all replace the disc with new ones, try to get the original disc or a good oe ones like ATE. make sure you do a proper wear in process for the pads and disc. replaced all fluids and bleed the system. you should be good to go.
the original brake setup is more than efficient to stop your car. adding too much front bias braking ie:- changing to 330 or other BBK will just affect the balance of the system. you front wheels will skid first before any sufficient grip is generated.
will 330 brakes bolt on without any modification? yes, however they are not easy to come by and cost wise, IMHO they are not worth it. anyway you will need the correct master pump to correctly match the setup as well, or you will find yourself pushing further to achieve the same stopping power as before.