1968 Chevrolet Camaro Engine knock

To see if it's an internal engine problem like a piston/rod bearing etc. Try removing one plug wire at a time while idling. If the knock stops then that tells you what cylinder it is and you can check further like compression etc. However this could be carbon buildup as well as they will make a loud noise often mistaken for a rod or bearing knock. If your oil pressure has been good lately then I'd assume it's not a rod knock. If it is carbon most dealers like GM and Ford have decarbonizer it's all the same so it doesn't matter where you get it. It also could be piston slap which will go away when it warms up. If you can't find anything have a local pro take a look at it maybe he can tell you better as we can't hear noises well on computer even if it's recorded.