I like the Catalina 27 inboards for a starter coastal or lake boat. They sail ok and at least they don''t have a cored hull. Have it surveyed and don''t pay a lot. If you really like it then you will want a bigger boat so keep in mind that this is a interim boat for coastal sailing.
The words atomic 4 and diesel don''t go together. The makers of the famous atomic 4 gasoline engine, Universal Medalist Marine, alsomade diesel engines. My guess is that it''s the A-4 which is a very good engine. But like Jeff said the boats not new so get it checked out.
I really like masthead designs with big genoas like that C-27. Jeff does not. I think for cruising the big genny is easier for me. I would rather roll up a 450 sq ft genny that I can reef also than handle a 250 sq ft main. So the Genny is my primary sail. On a fractional rig you don''t get much of a jib. Whatever. They are both right answers.