[Kunama]

Thanks for all the suggestions,

The Baader-Kunama-Takahashi adapter is ready for its maiden voyage.

I ended up going with 'Option 2' The Takahashi extension tube is now a
M55.9 P0.75mm > 2" 24TPI SCT converter:

Thanks to Graham, at Canberra Machining Company, the Tak tube was cut 39mm shorter and a 24TPI 2" SCT thread cut with an undercut at the the step to allow full engagement of the thread. Anyone in the Canberra area needing any custom machining, Graham is happy to do small jobs like this at reasonable rates.

Finished setup, actually the modification is intended for white light solar with the Baader wedge.