I looked for my NC Marine catalogs to try to find more info, but all I could find was this MoPar Marine parts book. It shows only a 251-no 265 under the Crown name. Hmmm.. I do know that the Industrial and Marine engines have a lot of differences compared to passenger car engines. I have worked on a few industrial engines and always had unexpected issues to resolve. Once tried to put a new 251 marine crank in a big forklift engine rebuild-rear flange had a different offset-Don't want to deal with that kinda stuff anymore!
Bob