Loud knock gets louder when the engine is revved

Bent valves do not make noise. Lifters do not make a loud noise. Your engine does not even use lifters.

The noise "stays at a constant sound and speed", and "it speeds up and gets louder". Without any other clues or the ability to listen to it myself, a good suspect might be a loose harmonic balancer, (aka, vibration damper). That is at the "front" of the engine and has the pulley on it that drives the belt. With the engine running, watch that assembly to see if it is wobbling.

Probably not. To post a video of the harmonic balancer you have to see it, so just watch it to observe if it's wobbling.

It sounds like a rod knock to me. It would help if you can post a video of the problem on youtube and then give us the link, then we can have a better idea.

Best, Ken

Yes, the engine basically need to be rebuilt or a new or used engine installed, sorry.

I have good news, its not a rod knock it sounds like you either have a broken valve spring or a a cam that has gone flat, start on the side that the noise is coming from and remove the valve cover, then grasp each rocker and try to move it to check for looseness. Some will be tight because they or in the cam lobe cycle. Turn the engine over by hand 90 degrees and check the others, then turn it 90 degrees again and check the rest.

Love the video BTW. Really helps, if you can rev the engine it see if the noise goes away which is another sign of valve train issues.

Best, Ken

Need to see what it is first, could be expensive if the cam is flat but only like $300.00 (US) if a valve spring is broken