The 50th. Anniversary Blackhawk .44 Mag used the .44 Mag size flattop frame.
The 50th. Anniversary Blackhawk .357 used the smaller flattop frame.
They both used the one-handed grip frame, though, right (XR3)?
You can still buy them new for just over 400 bucks: http://www.galleryofguns.com/Genie/...Revolver&cal=44M&fin=Blue&sit=Adjustable&pid=
If they used the XR3 grip frame on the .44, it would be one reason I wouldn't.