Originally Posted by Oranoco
4x4 Cossie brakes should fit under your 15's although some wheels won't allow them to go in. You may also need to balance the wheel slightly differently to give clearance.
Leave the rears alone as they are quite up to the job at hand. They look a little agricultural but they do work. Why change them for something more aesthetically pleasing that tends to cause more problems than they cure.
A good mate of mine still runs stock drums on the back of his 400bhp ZT monster FRST

I have Hi spec rears on mine

a nice little conversion if i do say so myself

altho with only 180 bhp tbh its not really needed but as i WILL be going for alot more soon, and my drums were fooooooked I thought i'd do something different
& yes jay cossie brakes will fit over 15's as standard cossie wheels are 15

but as oranoco said just check the offset