Could be piston slap when cold remember 4.6 had offset piston pins it was sup post to control that. I don't know if it was carried over on to 5.0. Now factory pistons had this but none of aftermarket did this
I thought I'd share this with you and this isn't from me its from the bearing manufactures.
First, itís essential to understand that bearings
depend on a film of oil to keep them separated
from the shaft surface. This oil film is developed
by shaft rotation. as the shaft rotates it pulls oil
into the loaded area of the bearing and rides up
on this film much like a tire hydroplaning on wet
pavement. Grooving in a bearing acts like tread
in a tire to break up the oil film. While you want
your tires to grip the road, you donít want your
bearings to grip the shaft.
The primary reason for having any grooving in a
main bearing is to provide oil to the connecting
rods. Without rod bearings to feed, a simple
oil hole would be sufficient to lubricate a main
bearing. many early engines used full grooved
bearings and some even used multiple grooves.
as engine and bearing technology developed,
bearing grooving was removed from modern
lower main bearings. The result is in a thicker
film of oil for the shaft to ride on.
Sorry for the long paragraph, its directly from Clevite's site
And I believe they should know, they fabricate these things LOL.
Anyhow after further examining the pic provided in this thread. It seams as ford either got lousy QC control in their engine plant where ever that might be. The pic shows poor bearing wear to be more specific poor eccentricity of the bearings. Channel this with too thin of an oil at star-up and the end result is what's in front of us on this pic.