od of 2wd water return spout is 7.88mm

od af 4*4 water return spout is 21.4mm

figures courtesy of dear old uncle tony

you'll have to get a 4*4 tank (only about £20 from ford) and then a T piece fitting kit and plumb into the existing water return from the turbo if you want to keep the swirl pot

theres been some class arguments about this being the wrong thing to do

ive run mine with and without a swirl pot and it makes no odds to anything as far as i can tell