On my 335 my hull anode is
150mm long by 60mm wide and 25mm deep.
The bolt holes are 80mm apart from centre to centre.
I got mine from Tecnoseal - 220AL.
It is Aluminum. But I am yet to replace it as there is still plenty left.
Bit of a minefield anodes. Apparently you shouldn't mix anode metals on a boat but it is hard to find only zinc as manufacturers are changing to aluminum now as it is cheaper.
I think it doesn't matter if you use different metals as long as they are not connected to each other?
Sailing in freshwater, use Magnesium only.
No doubt there will be someone out there who knows more about this.
Mike
Shemar 335/46