I found the cast block number as a '54-'55 261 on the Inliners site.
Screenshot - https://farm8.staticflickr.com/7550/15782968312_b6c8e2d7f2_c.jpg


It does have an older rebuild tag on it. So the head might be a replacement and the ID might be a re-stamping.

I'll check the date casting code on the head tonight.

Thanks for your input, Tim!