for the five minutes mine ran, the Harland sharp rockers were quiet. make sure you get the install instructions, I have my motor back apart because of the lack of instruction.
The spacers have to be ground to fit due to improper manufacturing, it is very simple to do but if you do not, you will be taking it back apart to check for damage. in my case it appears I have no damage, the rockers seized while at idle.
I am doing a compression test this week to check for bent valves but so far the lifters, rockers and rods are all ok. (checked travel of rods with dial indicator all are the same. removed lifters and rods and inspected all parts).
I was going to do the p400 but instead went with gep and spent the difference in roller rockers and the timing gear upgrade The gep and both upgrades were cheaper than p400. It only ran for 5 minutes with only one small easy increase in rpm to around 1500, as I was checking all fluids and it was coming up to temperature the motor died. I have no exhaust just a 4 inch elbow from the turbo and it was quieter than my 6.2 with the hood shut and the stock muflers. At this time I have no front fenders or hood. I think the two upgrades made the motor quiet.
What I read in forums prior to purchase was the gears make the timing more precise than the chain so you get less rattle from better timing and the stamped rockers have chatter where these do not so that is the reason for the quieter motor. I had the money to burn at the time and I think it did help. Also did fluid dampner.
my two cents. I will update my own post once the motor is back together. just chiming in here about the rockers since I actually own them.
Rich