Looks like you've got the bug
Yeah, my prop nut is made of aluminium. I've got a couple other outboards (including Aussie made ones) with the same prop nut, so it would appear this was a purchased part and not something made by Anzani. Anyway, having seen some of the work you've already done, it wouldn't have thought it would be too difficult for you to turn one up on your lathe.
Re the polishing. You seem to have found an easier way than me to smooth out the aluminium, so thanks for that.
What you've done so far looks great. If you want to take that to a super bright finish all you need to do is hit is with 1000 wet and dry to remove the scratches and work up to 1600 before buffing it with the grey and then the white polish.
You won't get rid of those deeper indentations, but that's ok. These things weren't perfect back in the day.