The OEM one comes with the extension panel/ Undertray as the V3 is much longer than the standard front bumper.
I'm no expert but as this is made in stainless,comes in two parts and has about 20 holes,all bolts supplied and fits perfectly onto my Zspeed undertray you would be complete Chimp to try and make one yourself.
Buy an original or a used replica one which has been previously fitted to a car so all the fettling and hard work has been done.