try ebay and only buy an alloy one,there a little more expensive but for the two you all ready bought ,youll easly get one and youll never have a problem with it and better cooling,make sure the hole rad is alloy too,some have plastic sides not worth a bollox.
when your changing the rad check all your pipe work for any wear ,as the top rad hose are prone to go bang,the samco kits are a great upgrade and look the business ,o and cheap enough on ebay