I think this idea is junk.
Got curious this morning and looked up AC compressor part numbers for an HC and a 6.4 and they are the same. Pretty sure the 6.2 and 6.4 blocks are the same in the motor mount/compressor area so thought maybe the HC uses a different boss on the block.
This picture from erict's thread makes me think they use the same boss:
View attachment 1716058432
That addition bolt hole below (above?) the rear AC compressor mount on the above picture is covered and can be used for the Holley swap mounts, so it isn't used for the AC compressor on the 6.4/5.7.
So, I don't think the FEAD is any further forward on an HC than it is on a 5.7/6.4. Somehow Mopar seems to have been able to fit the SC belt behind the FEAD belt. At least I think that is the case.
It should also be noted that the FEAD is further forward on a 6.4 compared to a 6.1 by about 1/2". There is disagreement on the 5.7 but far as I know everyone agrees that the non-VVT 5.7 matches the 6.1 and the 5.7 after '11 is a match to the 6.4. I believe the '09 and '10 5.7 shares the same FEAD spacing as the non-VVT motors even though it has VVT, but that is yet to be proven.