We have seriously listed and priced our '91 Classic, Amazing Grace, with HMY. The Yachtworld listing contains all of the particulars. Over the past 5+ years we have replaced just about every system on the boat from the refrigeration to air conditioning to the black water lines. The tanks, decks and genset are original and in good condition; Even the main engines are newer than the hull. The 315 Cummins were installed by the original owner in 1993, replacing the 300 hp that were original. I don't know why this was done, I just know these work well, about 2275 hours.
As to the why, I am interested in another boat and don't want two, or three if you count the Grady CC. My wife thinks I've lost my mind; she may be right.
Happy to provide detail of the upgrades. Full disclosure, our son is the listing broker. Yep, she's right.
YW link: 1991 Grand Banks Heritage Classic Power Boat For Sale - www.yachtworld.com