I'm having a similar problem with my 440 based 511. The engine builder speced a custom grind Comp cam. I had wanted hydraulic rollers due to less maintenance. Duration @ .050 Intake 243 Exhaust 251, 595 lift on 113 ICL using 1.6 Hughes roller tip rockers. When I started it up, it sounded like solids that were loose. I took the engine back out of the car and took it back to him. He pulled the heads and took them apart and checked everything. He has them adjusted 1-1/2 turns. Nothing wrong. I put the engine back in the car and it was just as noisy as before. I loaded the car onto my buddy's trailer and we drove the 120 miles to his shop. When I started it, he was surprised at how noisy it was. We decided to change to solid roller lifters, as he said that he was sure they would be quieter when properly adjusted. The car is at his place now, but he just had knee surgery. I don't know how long before the car will be ready.
I did find a tech sheet on Comp Cam's web site that stated that the hydraulic rollers tended to be noisy.

I don't know if your issue could be related or not. This came to mind when I read what you have going on.