The welded studs can easily be replaced with cadmium plated T-bolts. ( Generic and identical to those used in the 67 B'cudas upper and lower deck lid trims ). Assembly with these additional small pieces is a bit tedious which sheds light on why they put welded studs here.
So those T-bolts and pop rivets pretty much conquers the outer surrounds.
There are smaller studs in the inner surrounds with square heads captured in aluminum channel. If you ever had one or more of those studs spin inside the aluminum.... After 3 pairs of 67,8 grilles I assume there are even more issues I haven't encountered.
In my opinion, Your kit stops short of complete. Good luck with it.