I see a few errors in this thread. The 50th Anniv. .357's, New Vaqueros and Flattop .44 Specials share the same cylinder frame and cylinder dimensions that were first introduced on the original .357 Blackhawks back in 1955. The 50th Anniversary .44 magnum Flattop is a copy of the original .44 magnum Blackhawk Flattop introduced in late 1956 which was developed with a "large" sized cylinder frame and cylinder. The large cylinder frame has been in use across the board for the New Model Blackhawks, Super Blackhawks and large calibre Bisleys.
The Old Army is unique in design. The Old Army grip frames are "Old Model" components and won't interchange with a New Model grip frame unless one is adapt at making some changes in the trigger spring and cylinder latch spring areas. The Old Army grip frames were aluminum from '72 up until sometime in the mid 1990's when they were changed to investment cast steel. (Stainless Old Armys excepted, of course.)
One can, however, adapt a New Model grip frame to an Old Model revolver by fabricating a simple adaptor to carry the OM trigger spring in the NM's trigger spring slot.
flatgate