Hey Ed,
I've always felt like the engine grill is a little restrictive for an oil cooler but I have no technical data to back up that feeling.
Ruf did use something similar so i'm probably way off base with that feeling. Although I checked the pics of the valance I sold a few years ago and it looks more open to flow than an engine lid grille
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/906269-vintage-ruf-poly-lower-valance.html
But since the flow across the front cooler is a bit challenged due to the area behind it being somewhat of an obstruction, I think we want to get as clear of an opening as possible while still providing protection against debris.
The stuff Pegasus offers is really nice stuff at a very reasonable price. I have a sheet of their coarse mesh in 18x24 size that you're welcome to check out and see if you like it?
https://www.pegasusautoracing.com/productselection.asp?Product=3642