Bringing a bit more reality into the discussion. I took the proposal of
and took pictures of the already sandblasted saildrive and propeller.
In respect to coppercoating saildrive and propelle the critical area are:
1 - Cooling water openings in the leg of the saildrive
2 - Screw at bottom of saildrive (to change oil and do pressure test)
3 - Srew at the end of the propeller spinner
4 - Through-hole at the spinner
5 - Small metal pieces to not allow the spinner to rotate free against the axis by inertia
See also attached pictures.
There are 2 more screws to remove the lower horizontal shaft of the saildrive but these screws are covered by the anodes.
Assuming you would want to coppercoat saildrive and propeller. What would you do with these areas?
None of those have any bearing on the coating, and most of them only have to do with the propeller itself. The cooling water passages you wouldn't plug up (easy), and the oil change bolt sits on a flat flange with a o-ring seal. You wouldn't be coating the flange or the bolt, and even if you coated the bolt, it wouldn't prevent it from being removed.
I wouldn't put copper coat on my saildrives, but that is just my preference. I definitely would not coat the propeller with it. The reason is that the build thickness will change the foil shape, and there is no way the epoxy will stay on it. Soon, you will get a lot of pits and failure points, and once the edge is lost, it will start peeling. This, I say from experience.
Since your drives are blasted back to aluminum, you will not have good luck simply coating them with anything because they have oxidized by now and nothing will stick well without some more prep. You will either need to etch them with a suitable aluminum etcher solution and follow that with a chromate primer, or you can sand them back to white aluminum and immediately apply epoxy while sanding. This epoxy wet sanding will get the epoxy to good aluminum.
After that, you proceed as you like with antifoul of choice. Personally, I would not put copper on the drive regardless of what form it is in. If this was necessary, I would put a thick barrier coat of epoxy on it before the copper coat. I would not trust the copper coat epoxy solution to be the only barrier between the copper and the aluminum.