The castings for the oarlocks are beautiful and very serviceable.  If you want them to be a little special and take on the Bristol Yacht appearance, it’s going to take a little work.  This is a before and after.
;

We started out with a coarse 3M pad on an air tool.  This delineates the high and low spots.

Then, using a combination of fine tooth flat and round files, you gently work out the low spots.

The areas that need attention are readily apparent and just need a little patience to work then out.

Hard to believe this is the same casting.  It just takes a little elbow grease.   You can see the abrasions in the metal from the 3M disc that I used to take out the file marks.

OK, finally you get to use a material you are used to.  Remember, sanding is fun.  Start with 150 or 200 grit and work towards 400.

Finally, use the buffing wheel to get that high gloss finish you were looking for.  Go buy some Brasso and finish it off.   You will have many hours of quiet polishing time in the future.