[705jmguy]

Will share with everyone my experience with knock in my 305, the knock was not as sharp as yours so may not be same thing, it was running smoothly, good oil pressure, compression was on the lower side on all cylinders, not smoking or using oil.
Mine had a annoying knock at idle, was told it was the harmonic balancer when I purchased it, and of course that is not true as it has no harmonic balancer on the front pulley
Pulled the engine to make sure it was not a rod bearing, thankfully it was not, so decided
to give the engine a little spruce up so to speak, but not having found the cause of the knock as of now, had crank shaft checked for specs, on the low side but still in range, still no answer for the knock cause.
Was beginning to think it was my imagination at this point, decided to pull pistons, clean up cylinder walls and put in new rings and bearings.
Had the cylinders checked and found the problem, piston slap, the old girl still was running good no smoke even with the pistons slapping away.
Had to have it bored out over sized, had new pistons made as could not find over sized.
Before I purchased it was sitting for at least five years, not started, perhaps a little rust developed on the cyl walls and a hard start caused rapid wear on the walls causing the pistons to slap due to premature wear
Just my two cents for everyone info thanks