Welcome to the forums Elaine & Co.!
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Have you considered replacing the engine with another gas engine of the same size? That would be a more direct bolt-in replacement. Granted, lots of bolts, but easier and cheaper that switching to diesel. If you switch to diesel, in addition to the engine, you'll need to replace the entire fuel system. And if you change from a normally aspirated engine to a turbo-charged engine, then you need to deal with any vacuum driven items and provide a new source of vacuum. I have no idea how you would do that part, but there must be something out there that would work. One last question I can think of - will your transmission work with a diesel? As in will it bolt up to the engine ok, and does it need a source of manifold vacuum to help it know when to shift gears? I'm assuming it's an automatic transmission.
I'm not trying to discourage you, just provide a few things to think about. Can you do it? Sure - pretty much anything is possible if you throw enough money at it. Is it worth it? That's something only you can decide. No matter what you decide to do - welcome again and good luck!
And pictures are always nice!