Copper rod bearings?

[Ross F-1]

Somewhere in the back of my mind I remember reading that HD rod bearings were made with a high copper content, sacrificing conformability and embeddability for high load bearing capacity? I'm disassembling a truck engine and am kind of surprised by these rod bearings. I could believe that all the tin and lead is simply worn off, but they are very uniformly worn, no sign of lead anywhere, and were not particularly sloppy. They are stamped as Federal Mogul 1505 CAA pieces from '62. Looking at FM's catalog (Sealed Power now) that's still a good number, but no mention of special alloys.

The mains are dated '57, also FM, and look conventional, and not badly worn.

Ever seen rod bearings like this?