1986 Johnson 40hp sacrificial anodes

[BlueFightingCat]

J40ELCDE
G7100857

I recently acquired a 1986 Johnson 40hp outboard. It was used in lake water and now I plan to use it in the sea. So I want to change the sacrificial anodes to aluminium.
I am trying to identify where all the anodes are placed. The service manual is not very helpful with this. So I looked up the "exploded view" of the gearcase here:

https://www.boats.net/catalog/johnso...elcde/gearcase

It seems there are 2 anodes (parts 77 and 80). 77 is easy to change but I am wondering about 80. If I have interpreted the picture correctly it is in the gearcase and I would have to remove the lower unit. I've looked up some youtube videos of the same/similar engines, but none of them seem to have this anode.

Before I remove the lower unit, I was just wondering whether anybody had any experience with this that they can share. Is anode 80 necessary? Should it be there in practice? Or will anode 77 take care of the job by itself?

Also should the trim tab on this motor be sacrificial?

Thanks

[ChampioNman]

You need both. Is 80 missing from your motor? From what I remember it is an external mount but it has been a long time since I have worked on one.

[BlueFightingCat]

It definitely is not on the outside of the motor and I'm reluctant to take apart the lower unit until I am pretty sure it's supposed to go inside. There seems to be 2 holes through which I can bolt the 80 anodes on the outside of the unit.
The exploded parts view seems to imply it goes inside:
https://www.boats.net/catalog/johnso...elcde/gearcase

[bighare]

Anode 80 is an external mount in the 2 holes you see. No gear we disassembly required

[BlueFightingCat]

Anode 80 is an external mount in the 2 holes you see. No gear we disassembly required

Thanks for the info. I don't have the necessary screws for it. Is it ok just to use normal "sea resistant" screws for that or do I need to use a specific type in order to avoid some sort of reaction with the engine and or anode?

[bighare]

Common stainless steel nuts and bolts will be adequate.