Reading the article I have never come across those Main caps but do remember some print on them now, I also have never come across a 1964 Hemi Balancer that was a thin balancer, not many 1964 Hemis out there I think 271 blocks were cast, have what Chrysler built for 1964 some place. Maybe a thin balancer for 1964 went on Nascar Hemis. 1965 motors have the thin balancer, All three of my 1971 installed production hemis do not have these main caps and all came with the stock thick balancer. You would think if Chrysler knew about these main caps in the blocks they would have a breaking point to when these caps were installed in the blocks that got these. But like everything else they only deal with a problem after it happens not before it happens and hope your warranty runs out but just how much warranty did you get on a Hemi Engine in a vehicle. I will dig that old yellow book out and read the complete section...