Enough info was provided to figure out these questions.
Lobe lift is just valve lift divided by the rocker ratio used, in this case 1.65.
With .616 intake lift divided by 1.65 you get a .373" lobe.
With .621 exhaust lift divided by 1.65 you get a .376" lobe.
And no, I'm not sure why anyone would think that's too much lift for a street car. I've run that type of lift on the street for decades with no ill affect, no spring changes, nothing.
As far as coil bind questions that spec was given at .830" so the springs even with a 1.65 rocker are .209" away from coil bind at their closest.
And with an install height of 1.735" and 1.750" I'd be highly doubtful that a retainer is making any contact with the guide, even if a positive seal installed.
Worth checking for piece of mind but doubt you'll find anything here. If Paul set those heads up I'd be confident they are spot on.
I agree with Paul, 6200 rpm is nothing for a 455 and should have no affect on valve train durability or stability.
Your witness marks on the original rockers however may have something to do with it, and from there the issue may have never went away even with a rocker change and more valve adjustments. Unfortunately now that they have been removed and changed there is no real way to tell if the witness marked rockers correspond to those pushrods.
At this point I'd just spend the money on a good one piece thick wall pushrod, replace them, adjust the rockers the way Paul explains, and move on with it.
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