We extend to you a cordial "WELCOME ABOARD !" Come on in, make yourself at home, we are a friendly group of enthusiasts, and we also appreciate the classic Chris Craft Roamer, Corsair, and Lancer boats too , as they are all on the same family tree and share much in common !
The only way you'll ever recover any of your diesel installation cost it at resale time. Fuel costs will never get you there, the delta isn't enough. The resale is totally skewed too, based upon the brand, hours, boat make, etc.
David Pascoe (notable marine surveyor) published an article, I believe I saw it referenced here on the forum not too long ago, about the myth of diesel power. Diesels work well in vehicles that stay warm and/or work on a daily basis. Of course, they work well in other applications too like yachts that sit around for months before running, but the point of the article was "buy gas" for most applications.
If you buy diesel, do so because you want diesel, and not because you're trying to pen out a long term payback, etc.
I'm with Roy on the repower. One look at that rusty ballast you have there, and his comment about "life is too short" really rings home.