The 45-70 and 444 Marlin are in the top 10 of the list. 458 Win. Mag #1, 375 H&H #2, 338 Win Mag. #3. 30-06 w/250 gr. rnd nose, #4, 45-70 #5.
In the hands of a competent guide, there is nothing more effective that a 375 H&H. A 350 gr. RN delivers 5800 foot pounds of energy out to 25 yards. No Brownie on Earth could stand up to a solid, well placed hit from one of these.
I would pick it over a 458 because it has less recoil and the shooter recovers much quicker for a followup shot. (I have had actual experience stopping a charge.)
As I understand it, a LARGE CALIBER hit to the vitals can bring a Grizzly down, but the best thing is to hit bone and take out a hip. That immobilizes her. A shot to the head might ricochet off and a shot to the hump will just piss her off.
This is all gleamed from the experience of others.
I agree with your cartridge choice, but getting a nice pre-64 beat up in the brush would be a shame. Seen what they’re getting for those suckers these days?
I had a 1938 Mod. 70 carbine in .30-06, made a nice profit when I let that go. Even had a Stith no drill scope mount and a NIB 2.5x Lyman Alaskan to go along with it.
Local gunsmith here in Alaska that modifies a 45-70 lever action into a specialised tool for bear protection.
.50 cal 450 gr @ 2050fps!
My 458 mag using the 530 grain load brings down a charging bull elephant. It’s overkill on the bears in my area... and I wouldn’t settle for less!