It all comes down to the way production was done back in the day. There are other posts on moparts about this. There was very little FIFO back when our cars were built. FIFO meaning is first in first out. Back in the day these block were stored in one location and the builder worker would just get the first block in line and he would not care if there was older casting date on a block. So motors get build until the last block was there and the last blocks were from a previous time and that might of been back as far as 11-11-68 that my original Hemi motor in my June 1971 Challenger has. My 1971 Hemi Cuda November 1970 built has a casting date of 1-21-70 like most of the 1971 Hemi E Body have between their frame rails originally. I also have a 440-6 motor with a casting date in January of 1970 on the block. It looks like Chrysler fired up the forge and started doing Hemi and 440 block in January of 1970. Most of these Hemi blocks were cast between January 19 and 27 or 1970 a few before. I have not every seen an original Hemi motor in a 1971 E body with a casting date after January of 1970. Would like to know if anyone else has ever come across an original Hemi block to an ebody cast after the January date 1970.