The gudgeon: I wondered why yours didn't have a strap around it as in the Irwin drawings. I would think you can have a new one made from the detailed drawings. The thickness of your gudgeon must be less than the OEM gudgeon or the two halves would meet based on the thickness of the deadwood. Obviously, make sure that's the case with the new one.
Q1: I would have the new gudgeon and strap machined out of the same material as the rudderpost--stainless I assume (only it should be 316L stainless--nothing less). I would make enough tolerence in the gudgeon so that you can install a delrin or Teflon sleeve. The sleeve can be in two halves, thin sheets cut to the insides of the two clam shells of the gudgeon. I would steer clear of adding bronze to that underwater mix.
The rudder tube: It is not normal, nor proper. Greg, what is the OD of the rudderpost and the ID of the rudder tube?
Q2: The McMaster tube if you can get the correct diameter would work fine. The diameter has to take into consideration an available hose diameter as well as an available stuffing box size--they all have to work together (which may be why the second hose was used in your boat--the old stuffing box no longer matched the diameter of the tube so it was "shimmed" with another hose, instead of replacing the stuffing box with the correct size.