Borrowed this from Savageshooter.com
1st. Gen Short Actions = 4.522" (1959 to 1987, staggered feed magazine)
2nd Gen Short Actions = 4.275" (1998 to 2006, staggered feed magazine)
3rd Gen Short Actions = 4.400" (2006 and up, center-feed magazine, not shown in photo below)
I'm guessing that eddybo is fitting a new centerfeed action into an older more common staggerfeed stock, or an intermediate action into a short action stock.