How exactly did you work w/ your lower? Did you do it while it was just the casing, or sit down under the transom n go to town?
i did it on a stand,over 2 months in the winter,i started with 36grit grinding,it is a green sand cast so its VERY ruff and holly,i took a belt sander to it also trying to smooth and straighten it,i thinned the skeg sharpen the nose and the front leading edge, da sanding 60,80, 120.220. 320.500,then took some polishing compound a buddy at nissan gave me 4 5 gall buckets of, i used old wool buffing pads, slinging compound,i even tried taking the 8in saisl buffing disk with white rouge,it came out pretty good from 5ft away, its still porious,pited, they would never come out being it that way all the way thru the metal,it lasted about 3-5 trips in the water and if it stayed over night it turned, Now I just use a mag wheel acid brightener and a scotch brite pad, turn it a bright silver,wasent worth keeping it up being I run in salt water once a year, Main reason I had just restored/paint/motors, redid everything on the boat and put it in a car show with my other cars that year.
Now other name brand outdrives should be easier to polish,The imco I had on another boat was easy