It's been a few years since reading about this engine, but fairly sure merc had a few problems with this motor. The block was of their design, and I think it used a cylinder head from the ford 460. Sorry, but I don't remember the exact issues they had, but it was only used for a few years. As far as boat motors built for low rpms, I disagree. Most cars run down the highway in overdrive at 70 mph, turning what, 2500 rpms? Give or take. A boat, which is working much harder (more friction) might be doing 25 mph at same rpm. Depending on the prop pitch. My last boat ran wide open about 52 mph at just over 5200 rpm. This was merc's max recommended rpm level. Mercruiser builds their short blocks pretty stout. How many hours did this motor have on it when it "blew up" ? What was the rpm's when he was "overspeeding it" ?
95' Grand Cherokee, bone stock, 4.0, limited. Used as winter vehicle and rainy days. Warm weather vehicle- 2003 Mustang Cobra w/supercharger.