Like much of the exterior of '60's and '70's cars, it was anodized aluminum. It will look shiny but not totally smooth like a mirror, and this is the anodizing process used by the manufacturer. I think literature calls it 'Brite Dipped', or some other way of saying anodized. Sounds like you got the right finish. If you ever see a very original car or a piece of old trim that is new in the packaging (NOS), then you can see what the original Brite Dip looked like.
Trim that was stainless steel, anodized aluminum or chromed metal was all referred to in Chevy II literature as 'bright metal'. The GM Heritage Center site breaks down which trim was which in the vehicle information kits for each year. Link below.
Access free vehicle information kits (PDF downloads) for General Motors vehicles. The kits are part of the GM Heritage Center archive, including archived documents, artifacts and assorted automobilia from General Motors.
As Ally mentions above, you will never get a mirror, chrome-like finish on aluminum trim that has been anodized. Over many years the anodizing will also deteriorate and perhaps even wear off. The only way to fix this is to have the anodizing removed and re-done, or to remove the anodizing and polish the bare aluminum. The latter will provide a closer finish to chrome, but is labour intensive to maintain in that condition, like polishing very 10 days.