tanoose,
The subject on the Savage Model M came up about a year ago and should you care to try, you can see for yourself that in fact, there is no such animal. Now don't get your britches in a bunch..........there's an answer to all this found in Murray's book "The Ninety-Nine" A History of the Savage Model 99 Rifle, revised 3rd Edition.
On pages 3-70 and 71 is the description and photos of the model DE for Deluxe Edition w/ monte carlo style stock introduced in 1965, and discontinued in 1970. No one knows why the factory called/labeled them model "M" but it is believed to have indicated Monte Carlo buttstock. Model Designation....some were marked Model 99M on frame ring or barrel right-hand side.
Jim