I am thinking of the Grote 26012-5 black mirror kit. The mirror has rounded corners and most of the mounting bracket is black. It looks like an older style to me. I have not been able to find any pictures of the original west cost mirrors offered by GM.

Shane
1959 Apache 3100 Fleetside
1959 Apache 3200 NAPCO
1957 Chevy 5700 Low Cab Forward
1959 GMC F370 LCF
Another 1959 Apache 3100 Fleetside
1959 Chevy 5700 LCF
1946 Chevy 1/2 ton
1958 GMC 600
1974 Elcamino SS