CaptHead has very sound advice here, I think. While many people have converted gas boats to diesel, particularly Tollycrafts here in the PNW, the big question is always if the gain is worth the cost. For some boats and for some people, it is. For others it's not.
In this case, especially as it's a Carver, I would think the ultimate cost would never be recouped in the value of the boat in both dollars and intangible value.
Were this me, I would never consider a gas cruising boat in the first place and so would keep looking until I found what I wanted in a diesel boat.
As it's not me but you, only you can judge the suitability of this particular boat to what you want to do with it, how this boat fits your financial requirements, and so forth.
If you were talking about a high-quality vessel like a larger gas Tollycraft, which is an outstanding boat in terms of quality and construction to begin with, the cost to convert it to diesel may be well worth it, particularly if you intend to keep and use the boat a lot and for a long time. I doubt you would ever recoup your cost investment even with a Tollycraft, but you can't really put a price on the added value, safety, ejoyment, pride of ownership, etc., etc., etc. of the now-diesel-powered boat to you.
But since the boat you are considering is not something like a Tollycraft, and if you decide you absolutely must have this particular boat, I would strongly second CatpHead's suggestion to stick with the boat's as-built gas engines. In my opinion this particular brand is not worth throwing that much money at in the form of a diesel swap out of one gas engine, let alone two.