1960 Apache 40,

Although my guesstimates have been running poorly as of late, I will say that your explanation isn't consistent with a bad rod bearing in my estimation.

You should be able to make a rod knock at any RPM if you float the throttle. It wouldn't be necessary to bring the engine up to 1300 RPM. Have you looked at, or listened to the crank pulley or the water pump pulley. Wiggle stuff around a bit.

Stuart