I'm guessing anything the Model 8 was chambered in would be considered woefully inadequate It was chambered in .25 Remington, .30 Remington, .32 Remington, .35 Remington, and .300 Savage. All of those (especially .25 Remington) would be considered marginal at best these days for grizzly (of all of them, I'd pick .300 Savage).
I wonder what you'd get today if a you asked a firearm manufacturer to design for you an autoloading rifle for brown bear defense.
If I was hunting, I'd get a Browning BAR in .338 Winchester Magnum. 4000 ft-lbs of energy at the muzzle!
On the other hand, if it was strictly for defense and I didn't have to pay attention to game laws, I'd use an AR-10 in .308 with a 20 round magazine.
On the other hand, if it was strictly for defenseBecause the number of grizzly sighting have increased where we vacation in the Idaho panhandle, I picked up a defense gun just this week: a Marlin model 1895 GBL 45-70. Plan to load it with Buffalo Bore or Garrett Hammerhead ammo when in grizzly country. For close range hairy situations with a bear, the gun has few equals in terms of putting a wide, deep hole in an aggressive animal. Plus, the lever action makes for quick follow-up shots. There is a reason that these guns are so popular with Alaskan bush guides. It wouldn't be my choice if I were hunting grizzlies but inside of 50 yards, nothing will kill them deader.