Lend me you ears

Hearing someone else's slant-6 engine won't help you as much as you'd like—they vary more than common sense might suggest, depending on explainable stuff like different camshafts (factory cams not all alike), amounts of wear, grades of oil, skill and talent of whoever last adjusted the valves (and how long ago), and how hot the engine is…

…and unexplainable stuff along the lines of why some of these cars have rock-steady charging no matter how much neglect they've seen, and other cars, seemingly identical, have flickery charging even after every component, wire, connection, and ground in the whole system has been gone through with a fine-tooth comb.

All that said, the main reason why the Slant-6 has a reputation for "Aw, that's normal, they all go clackity-clackity-clack" is because most of them don't get the valves adjusted as often or as carefully as should be. Your valves, to my ear, are loud enough to warrant readjustment. Whether you readjust them is up to you.