Hmm... Sounds like you had or are thinking of one of the fairly recent short actions? The short action Savages have had at least 3 different screw spacings, although only actually 2 action lengths. The link I provided above gives a good summary as to when the various changes were made and why. To the best of my knowledge, however, the long action Savage has always used the same action length and screw spacing of 5 1/16".
The staggered-feed mags actually were/are still used for 223 Rem and 204 Ruger in the 'standard' rifles. Don't know why, but they didn't move those to center-feed mags when they changed everything else. They may have moved them by now. I don't know as I don't follow Savages so closely now as I once did.
Anyway, to the OP: The links and website I provided are the best one-stop source I know of for specific and detailed information, but basically you could probably make the change, but it wouldn't be worth it.