Here is a link to a Redhawk owners manual, not sure what year(EDIT - I just noticed the manual is 2009). I found on page 27 a statement that says:
"NOTE: The Hammer Pivot Assembly (Part No. H01600 or KH01600) tab fits into a mortise on the right side of the frame of most of the Redhawk revolvers. However, during a change in production processing of frames in 1983, several thousand frames were made with the mortise on the left side of the frame. A Redhawk revolver having the mortise on the left side of the frame is in all other respects the same as the version which has the mortise in the right side."
It doesn't say why they changed sides, but I found it interesting that they mentioned it.
Redhawk Owners Manual
