Cyclic hotline makes a good point about FAA certification. MAF would probably be better off soldiering on with the avgas guzzlers until Cessna or similar start producing a diesel engined production aircraft. I do not think this is that far away. At least then you will get a new airframe as well as the engine.
The cost of mods to CAA standards has to be seen to be believed. In the early 80's a simple long range tank installation which already had an FAA STC cost over £5000 to certify. Those index linked pensions have to be paid for somehow!!!!!!!!!!!!!