As you have mentioned, I would have concerns around parts availability. We are talking about a 50yr old aircraft and I would also worry about corrosion. Rare to find an ALWAYS HANGARED aircraft of this age and a really thorough pre purchase inspection by an independant Lame goes without saying, but i see from your comments that you are very experienced as a builder and know all this anyway.
I keep coming back to the 182 and while its not as fast as you want, you wouldnt be too much behind the Comanche over a 2 hour flight.
I havent seen a Comanche at Bankstown Airport in a long time, but they must be around somewhere.
My concerns would be age, corrosion, parts, condition of Instruments and Avionics which may be original, and payload.
Keep us informed with your search, hope it all goes well.