So for the fenders which came with rally vents already installed .
The rally vents were approximately 3” deep into the interior of the car so my metal guy cut a step in them to clear the footbox , then I came up with the mesh in behind idea so he trimmed them off flat at about 2”deep (which IMO looks way better) and then he Re welded the blades to secure them and did the wrap around strip over the mesh edge to both hold the mesh in place and also add more rigidity to the whole vent assembly . (See previous pics) . The grill and wrap around strip is a tight press fit but also has set screws on the three corners for extra security so no visible fastners . They will only be fitted after painting so the stainless mesh can be left polished .
Also on the passenger side the brace that goes between the inner fender and footbox was removed and repositioned lower down so you can’t see it through the grill /rally vent
For the front oil cooler grills.
My metal guy made an aluminum frame for the mesh (see previous pic) and there are tabs of material welded inside the shroud by the sides and between the openings to accept , sheet metal screws , nut and bolt , nutsert with screw , body clip with screw , whatever I decide is easiest to hold the mesh frame in place .
I made the metal hoop/forms for the openings but we decided to only use them to shape the openings , they are not left in place inside the shroud . The shroud material is rigid enough as is it’s not structural feature and the openings etc actually make it more rigid .
I also didn’t want the dissimilar materials issue of having a steel hoop trapped in behind the aluminum .