i duno just pay attention to the little details.. like the casting marks in picture one.. that line fin that runs down the center of the top.. at the front of there is a casting mark comin off the front of that and off of each side on the real one.... also the fin on the fake on in picture 2.. looks quite a bit thicker then the one in the first pic.. they dont really give you much to go off of on the HKS link.. even the pic of the boxes.. they are identical from what i see..
like i said though.. you cant just go off of a flange that i gave ya for the reason of you thinkin i may be a knock-off..