I wasn’t asking if you thought I was right. I wasn’t guessing. I was telling you what these numbers mean. But hey, you never believed me on other items before, so here is your proof today. Notice how the build date doesn’t appear on the stamped pad until 1960 model year.

Pardon me all to hell for encroaching on your area of expertise but I wonder if you noticed the contradictory info in your posts.In a previous post you declare "[9004 is not a build date it is a serial number," but in the chart you posted it shows a date on the top pad. I highlighted the '61 info you posted. If the 9004 is, indeed, a serial number, it doesn't fit any serial number format that I'm familiar with. Explain? Or is it a sequence number rather than a serial number?

Notice how the build date doesn’t appear on the stamped pad until 1960 model year.

The subject engine is a '61 so, accordingly, the date is on the pad.

A 1961 will have R41 with the 3 missing.

I think the confusion here may be that the reference materials say the block casting number is for a 1961 413, but the ID stampings do not match anything from 1961. It could be that the block was cast in 1961, and the stamps on the ID pad are just wrong. It could also be that the reference materials are incomplete, and the casting number could have been used in 1959 and 1960 as well as 1961.
If the casting number is correct, the engine is a 1961. If the stamping is correct, it is from a 1959 300E. It wouldn’t be the first time reference materials for casting numbers was wrong or incomplete, so I’ m leaning toward this being a 1959 300E engine.