Here's a picture of Keith's 99T with a factory installed G&H side mount. As you can see, the screws are all but invisible. They charged a pretty penny for the install..
Heck, you can STILL get this mount for a Savage 99. They still make it. Probably about $1400 for the mount and mounting it.
“The Savage 99 Pocket Reference”. All models and variations of 1895’s, 1899’s and 99’s covered. Also dates, checkering, engraving.. Find at www.savagelevers.com