While I'd never modify my M99, I wonder how much weight you could save by shortening the barrel as compared to a substituing a synthetic stock for the original wooden stock?
If you have a 24-inch barrel & take it down to say 22-inches... or even 20-inches... and hollowed out the wooden stock somewhat by increasing the diameter of the bolt-hole that goes from the butt-plate to the bolt holding the butt-stock to the action, you may be able to save more weight than going to one of those ugly synthetic stocks.
By doing this, you'd retain the good looks of a fine rifle & you might accomplish the same goal as going to a synthetic stock.
Playing the devil's advocate, shortening the barrel and removing some of the wood inside the original stock would probably change the rifle's "balance"... possibly making it a bit more "barrel-light"... depending on how much barrel you cut off. Of course, exchanging the wooden stock for a synthetic stock would do the opposite thing, i.e., you'd make it barrel-heavy.
However, if you exchanged the wooden stock for a synthetic stock
AND shortened the barrel, you could possibly retain the rifle's fine balance.
In any case, "sensed" recoil would be increased due to the rifle's overall weight loss and the rifle's value may be considerably decreased by such modifications of the barrel & original stock. Whereas by substituing the synthetic stock for the original stock, you could always go back to the unchanged original stock with nothing lost.
Unfortunately, you're between a rock & a hard place.
Good luck in whatever you decide to do...
Strength & Honor...
Ron T.