Please help me diagnose this 273

Rule number one of diagnostics, never assume anything. Best way to tell mechanical condition without a lot of work is to do a leak down test. This will absolutely tell you if you have a valve/guide and /or ring problem. With that info you can start to do your repair. Biggest lies in automotive, Just been rebuilt, just needs the carb or timing adjusted. Never believe anything you have not checked for your self. Something I remember hearing many years ago from one of my early mentors,"Never believe anything that you hear and only half of what you see."