One must always remember that the spring pressure is not directly below the attaching rocker shaft bolts.
There is that rocker arm which multiplies the 650 lbs (example) of the spring. The rocker arm is a lever, multiplying
the force as seen by the rocker shaft/attaching hardware.

With a 1.76 ratio:
600lbs of force at long end of rocker/lever.
600 lbs X 1.76 = 1056 lbs of force at the short side of the rocker/lever.
The pivot point (shaft centerline) sees 600 + 1056 lbs of force.

No wonder T&D race rockers do not rely on the 4 mounting bolts.

Tunnelwedge must have been born on the moon - or has zero experience with FE blocks.
I have seen several that had end to end and side to side issues - as Brent has mentioned.
And I haven't worked on many - certainly far, far less than Brent has.
FE blocks from Ford were nowhere near parallel or square - and it didn't matter for 8.5:1(9.5:1 LOL 2bbl) and 9.5:1 (10.5:1 LOL 4bbl) FE's.

From my research:

"Most stock street engines will run smooth enough if they are balanced to 1 oz. (28 grams), although many late model engines have much tighter factory specifications (as little as 4 to 6 grams). For a high-revving performance application, aim for the recommended 2 grams or less."

Which category would your engine be?

Run it!

From The Autotec 4032 piston instructions:

Applications Bore Range Min. Clearance
SB Applications 4.000-4.200 .0025-.0035+
BB Applications 4.200-4.600 .0035-.0045+

These are minimum values. You are at the minimum recommended on 7 cylinders.
I like to be a little above minimum recommendations. For me 0.0045" would be my happy place.
I would be honing the 7 other cylinders for more clearance - most certainly any that were below 0.035"

The specific piston measures the same as the other 7?
Skirt coating could certainly be used to fix an issue. Calico is a very reputable company.

Lack of oil can also lead to valve tip failure.
The oiling helps lubricate as well as cool the interface between the valve tip and roller.
Lack of oil would certainly heat up the area to the point of annealing the valve tip.

I would verify that you are getting enough oiling to the rocker arm roller and valve tip.
I am now leaning to this reasoning.

I know that some go to great lengths to reduce oiling to the rocker arms in FE's.
Verify oiling to rocker roller and valve tip.

Valves without enough hardening depth.
Sometimes caused when valve tips are ground reducing hardened depth.
I have had 1 valve out of 8 show similar grooving after <500 miles (800lbs open) These were Ferrea Competition Plus valves.
Replaced the one valve and then went to lash caps.