Hey there,
My rudder isn't nearly as bad off as yours was, but this project is definitely on the horizon for me. I've studied my rudder thoroughly and came to a completely different solution for removal than you ultimately did and I was wondering why you choose the route for removal that you did. Perhaps I'm missing something? Perhaps you wanted a different type of rudder?
What I came up with:
The attachment of the original rudder blade as best I can tell is accomplished via 7, very long and heafty, flat head machine screws. These screws pass through the rudder stock/axle, a section of the rudder blade and then into an resin encapsulated nut in the blade. Further attachment is made via a pair of rudder gudgeons that pass over the rudder stock/axle and are thru-riveted to the rudder blade.
My plan is to first drill out the rivets in the gudgeons, then fabricate an offset screwdriver that can pass between the rudder stock/axle and the keel, and then unscrew the screws. This will require each screw to be backed off a bit, the rudder pulled out, and then repeat until they have disengaged from the nuts. Once free, remove the rudder blade, leaving the rudder stock/axle in place.
ALTERNATIVELY, I may just dig out the resin encapsulating the nuts and just take the nuts off the ends of the screws, which honestly sounds like it might be easier than plan A. The offset screwdriver will be required either way since I'll obviously still need to engage the heads of the screws to get the nuts off. The rest of the removal would be the same.
Once the rudder blade is removed the rudder stock and axle become two independent components which can be inspected and repaired as necessary without the need to drop the whole unit as a single assembly which as you found out came with its' own set of complications.
Finally, fabricate a dimensionally correct, direct replacement fiberglass rudder blade and install as the opposite of removal of the original.