I fitted a genuine rs500 cooler as I bought it off a mate for the same price as a new alloy 500 style 1 would have cost, from what I have heard the Radtec ones are the next best and closely followed by the forge ones.
eceryone I know seems to stay clear of the pace coolers.
on and the only mod I had to make to fit mine was making the pipes fit, as the 500 has larger hoses than std, but all the alloy ones have std size hoses, so no mods needed afaik