[davepl]

I had to use spacers on a motor that had roller rockers. I'll stick a photo below. As you can see I was trying not to draw attention to them.

But for stock rockers, unless the baffles or drippers or something are bent, it should be fine.

You might want to get a mechanics stethoscope, or even a piece of PVC pipe and listen and see if you can narrow down the location.

Also feel along the valve cover; if you feel any tapping, there's something interfering.

However, when you see hoof prints, think horses, not zebras. Maybe there's something simpler, like a dirty lifter or loose rocker?

All my big blocks are quiet, or at least quieter than everything else going on when they're running!