Hello Nick,
Congratulations on your Tartan acquisition!
In 2016, we purchased Tartan 33 #107 which also needed the rudder replaced. We were actually able to purchase the rudder through Tartan, though it came from Foss.
When shipped, what the Washburn (WI) Marina technicians discovered was that the new rudder post had an outside diameter of .11" smaller than the original removed. That difference was unacceptable.
I was able to connect the marina with Tartan, and in discussion with Art Averell and Tim Jackett, the solution was to use UHMW tape to wrap the post and resolve the difference. A seemingly beautiful solution that has lasted for about 4000 nautical miles thus far with no issues.
I am providing the manufacture web site (at the time) her, in case needed.
McMaster-Carr
Good luck!
Dave Werner
T-33 "Yiamas"
Muskegon, MI