TF :-
Is it really possible, both technically and economically, to keep these types of historic aircraft airworthy in civilian hands?
The pertinent word is 'keep'. There is no reason to believe that any ex-military aircraft is airworthy unless the records accompanying it prove it to be so. The appropriate records for example of one type were found to be so much sodden pulp, stored as they were in a shed with a collapsed roof. Even if they were intact and readable I doubt they would have been of any use, because airworthiness is a matter of continuous record and audit. Break that process of continuation and airworthiness is lost, as was shown in the scandal of the ACO Gliders. Those that managed to fly again had to be fully dismantled and rebuilt IAW with the regs. Just doable with such simple airframes (though even then scarcely economic), but with a FJ? Forget it, keep them in museums for future generations to see unless they are indeed airworthy and can be proved to be so. Good luck with that!