NACA front cowling

I want to improuve my cowling on my Vixen serie 5 and I am going to use a Naca on the lower front like on the series 7.

Do you know the size of this NACA?

Hope these help:
https://www.facebook.com/#%21/photo....type=1&theater

• https://www.facebook.com/#!/photo.php?fbid=10150260793486270&set=pu.1326067862 69&type=1&theater
• https://www.facebook.com/photo.php?f...type=1&theater

https://www.facebook.com/#%21/photo....type=1&theater