Cessna 337's? You could do it. Again you need new flying surfaces. But, it's not econimcal. Nobody is going to pay $800,000 for one. I have seen the pictures of the 210 and it looks new. Everything is replaced except good rivets.
On the -703 engine: They are only using a few cases on the engine, NONE of the rotating parts are used. They are all new. It would be a waste to send a 703. All of the unused parts are scrapped even if they are servicable.
Sas: The idea of the 210 is for Guard use only flying very few hours state side. The program is the same as the Navy TH-67. Parts are simple to purchase without all the big contracts. They can be purcased in small quantities.