if its just the crank key area----------the later LT engines don't even use a keyway in the dampners/snout but do fit on very tight---You need an install tool kit to put those Chev dampners on properly and that doesn't just mean a big hammer and block of wood-


You can start and run the engine without the front cover or dampner /pulleys to verify that the knock/noise is gone-----------if it is then why not try a replacement dampner installed correctly?