I just had a 1 1/2" x 1/4" upper gudgeon SS bolt break off inside the transom and the 1 1/2"x 5/16" other upper gudgeon SS stripped out the threads in the aluminum plate. I cut a hole for a 4" curved access hatch and tried to remove the rest of the broken 1/4" bolt from the inside. It was corroded to the aluminum plate, so by using a vise-grip, I broke it off flush with the fiberglass inside of the transom.
The upper gudgeon was not vertically supporting the rudder casting and had been located ~ 3/8" above the rudder casting (the lower gudgeon was vertically supporting the rudder casting). Therefore, I was able to lower the upper gudgeon enough to re-drill the holes without hitting the broken off 1/4" SS bolt stub. I filled the 1/4" and 5/16" holes with thickened epoxy and re-drilled 1/4" holes through the transom about 5/16" lower than the previous holes. Then I used 1 1/2"x 1/4" SS bolts, 1/4" SS fender washers and 1/4" SS nylocks to secure the gudgeon (after gooing up everything with RTV).
I made the mistake of putting the center of both of the 4" access hatches about 13" from the rudder pins. This made it hard to see the inside of the transom or work on it (I had to use a flashlight and mirror). Fortunately, I did all the work to the gudgeon, before RTVing the access hatches in place, otherwise, I would have had a hard time getting my hand far enough inside to make the repairs. Also, lowering the upper gudgeon made it easier to use fender washers on the inside since there was the original 3/4" bead of resin/glue at the interface between the the top and sides of the hull just above the original holes for the upper gudgeon.
Some things I learned from putting in the two hatches and repairing an upper gudgeon:
1) Yes you can lower your upper gudgeon and re-drill without affecting your rudders.
2) The closer the access ports are to the transom, the easier it will be to do any repairs. Using a mirror and flashlight is no fun.
3) After you cut your holes for your access ports, do all your transom repairs before installing the hatch frames. It will be easier to get your hand and tools in/out.
4) I think 5" access hatches would be too big. The original ~ 3/4" bead of resin/glue at the top/sides interface of the hulls will get in the way.
5) I sealed the foam edge of the holes for the access ports with resin so the foam will not get wet. I waited a day for the RTV seal between the access frames/hulls to set before drilling holes for the frame's bolts. I also used longer SS bolts, washers and nylocks (all smothered in RTV) to anchor the access frames.
6) My hulls are not the same. The left hull has a "82 F" stamped on it's transom and the right hull is blank. The left hull has white smooth foam with a 3/4" black bead of resin/glue. The right hull has yellow, porous and stiff foam along with some red resin/glue inside.
Sail # 88863