Worn engines normally turn more easily than new ones. If it is more difficult to pull the starter than on other similar Briggs engines, and it has nasty internal noises, it sounds like it has a serious mechanical fault. The 65 psi compression test result would be within the common range for a well-worn Briggs, but unless you repeat the test with the teaspoon of oil added, that's all it tells us.
I suggest you remove the starter and rotate the engine by the flywheel fins (with spark plug lead disconnected, of course). See if you can find out more about this clunk. Also watch the piston while you rotate the engine slightly backward and forward. See if there is any lost motion when the piston is in the middle of its stroke.
