OK, I don't understand all of the mystery and hand-loading ying-yang I'm seeing here.
Can 't you just go to the website of Buffalo Bore or Garrett, and find a super-loaded .45-70 round, with a high quality premium deep penetration bullet, that is specifically designed for big bear?
Why does everybody try to re-invent the wheel?
One thing is for sure, with the route you are taking (handloading) the first shot on a grizzly at close range will be your first "experimental" shot on such an animal, and may be your last. Why risk it?
Also, I'm gonna bet that if you go to a few gunshows, you will find a beat-up Marin lever action in .45-70 or .444 Marlin, for about $350. Why in the world would you risk getting your face ripped off for a lousy $350? If you go this route, then when you return from your trip, you can always sell it, and get most of your money back.