You need conversion hoses to fit them, the MK4 caliper has a banjo-type connection.
if your mk2 is post 87, the fitment is the same for the handbrake cable, if its pre87 then you just fit them upside down. Problem is the bleed nipple will then be on the bottom, so you have to take em off & hang em up the right way to bleed.
They don't offer any advantage over MK3 calipers except they're a bit lighter, so dont bother unless you find em really cheap.
Plus even though they're aloy they still corrode too, so make sure you paint em if you find a set otherwise they sieze up, and make sure the bleed nipples are freed off because they sieze in very easily cos they're steel!
Edit: MK2 discs n pads fit straight into the MK3 & MK4 calipers
