Using an old micrometer, my original grille thickness reads about 0.042... the repro is 0.023. Not sure how accurate the micro is but even if it's off a bit the original thickness for sure measures about 2x the repro. Pretty thin and easy to distort. I'm still looking for a good original and will change out the repro if I find one.
As for rivets, I've seen pictures of solid rivet heads that are supposed to be original. Looking again at my old grille, a couple original factory rivets still on brackets have a hole in the center of the head and look exactly like stock Surebonder aluminum pop rivets I picked up at Menards. Side by side, can't tell them apart, though the bottom of the replacements bulge a bit more after install.
Sure learn a lot on this forum. Fun, and aggravating at the same time.