I am currently building a pair of 158s. With great reluctance, knowing that if I screwed it up, I would ruin an irreplaceable nose cone, I finally ordered the Indycals grille: https://www.indycals.net/parts/f1parts/50alfa158.html. Once the grilles came, it took awhile to talk myself into cutting into the plastic, but once I did, I was totally pleased with how easy it was to fit the grille and how great it looks once in place.