I just asked my IA about installing the GTR-200 and he at first said - "well it has to be TSO". Then I informed him how the King KX-170 has never had a TSO and he was like "Hmmm, really? Guess I never thought about that". A few minutes of back and forth and he said "Go ahead and order it".
So it does not hurt to ask and you may just get a good response from your AP/IA. My plane is going in for annual this week and he is the one signing off, so I should be all set. Time to get this old Narco out of the plane.
Next step may be an AV-30 and remove our vacuum system. I think our heading indicator is going bad and this plane will never fly IFR.