Chrome arch...... take out one screw, put a pice of wire inside hole
such that the wire end has a hook long enough to latch the unexposed threaded half. I don't know if it has this.
Remove or loosen another or others, and do likeise with wire. At some point when it is loose, you ought to be able to shake it a bit and determine if it has the threaded halves behind the body shell.

At all times make sure the wires are inside so that the back threads don't fall into body panel.

Find a way to eventuallt slip the chrome piece off the wires while keeping the hooked ends inside body.
That is how I changed the door latch/strike plate , which does have the threaded plate behind the body panel.

Use your imagination

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD