there are plenty of posts on here about gsxr 600 4-pots, the general consensus is to not go for gsxr 1000 6-pots (BTW you will need to search around the forum to find the correct models/years) at least not with the stock zxr 400 master cylinder up front.
if you do go for gsxr calipers i think you need sleeves made up as the mounting bolts are wider than the zxr ones?? again browse here, its all been asked before. Ebay also sells the spacers for the gsxr conversion...but after rebuilding my own calipers, new lines and new master cylinder internals my bike (after extensive bleeding) loves stoppies...i dont think better brakes will really accomplish that much, unless its solely a track bike.
if you are intent on fitting radial brakes you will need, new forks with appropriate mounting points, possibly new headstock, probably some spacers making up for the front wheel/new front wheel...seems slightly pointless for a total saving of ~1kg to me

UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said
