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Welcome. That sounds terrible. Take a long screwdriver, put the handle to your ear, then touch the tip to areas where you think the sound is coming from. It will act like a stethoscope to pinpoint the sound. Or if you have a Harbor Freight close by, they sell a real one for cheap.
I hate to make guesses, but if it's in the area you think it is, the most likely problem is the valve train. Either a cam chain got really loose, a valve bucket kicked out, etc. I'm assuming the rattle increases in step with the rpm? If it doesn't, then it could be something in the exhaust.

 

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So to make sure I understand, when you increase the rpm of the motor, the frequency of the rattle stays the exact same? That is really odd. If it were the timing chain or something similar, the speed of the rattle would increase with the motor rpm. That to me kind of rules out things that rotate with the engine. Even the exhaust flapper would change noise as the motor speed increased. Did you try pinpointing the noise with the screwdriver or stethoscope?

 

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Are you sure on the 33.5 ml of oil? That doesn't sound like it had any oil put back in it. I would think there would be more than just the one noise coming from it since you were riding it.

 

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That sounded like an awful heavy tapping for a valve. Plus they tend to tighten as they get more miles on them, not looser. At least that has been the experience of the few on here that have adjusted them. Mine is just short of 40,000 miles and they've never been touched. I really hope it is something that simple, but at least they can have a good look at it while they are in there.

 

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It's unbelievable that a dealer wouldn't want to do that. Guess they don't need the money? It's a job you can do yourself if you have the skills, tools, and the service manual. Or there are a couple guys on here that can do it for you, but none that are very close to New Orleans.

 

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Is that mount at the end of the cam broken? I agree with Slave, that is awfully dry unless you've already cleaned it up.

 

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The push pin mod involves grinding 3 flats on the sides of the clutch push pin to allow more oil into the clutch basket. This helps fix the clutch shudder issue. But it's been said, and maybe even proven, that grinding too much off and letting more oil into the clutch reduces the amount of oil going to the heads. That may or may not be what happened to yours, but it sure looks like there wasn't much oil getting up there.

 

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Wow, that's definitely from oil starvation. I'm flat out amazed it was still running. Hope you find the parts to fix it. Wonder what the other head looks like?

 

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That is something I've never done, so I can't help. Sorry to hear about your mechanic passing. Do you do Facebook? BigpapaXCT is on there, his name is Harris Horwitz. He's a great guy and is always willing to help. He doesn't get on here that often.

You can also try Matt, or FuturR on here. His phone number is in his signature. Look at the MAM meet thread, he started that.