I know dozens of people that have and pack Marlin Guide guns in 45/70 mostly and a few with 450 Marlins.
I'm a bolt rifle guy and had my final 458 Win mag built in 94/95 . Built on a stainless Ruger M77 Mk2. Its killed tons of brown bears all in an absolutely wonderful way.
I had a Marlin 45/70 . But didn't like how it would buck the action open with top handloads. And it was blued and wood stocked. I knew it would end up looking like a piece of old rebar on a piece of drift wood if I kept taking it with me in the skiff so I traded it on a stainless synthetic Model 70 338.
Skiffs and 4 wheelers and salt water and generally just being with me out in the brush is kinda hard on stuff.
Now that I live in The Interior. It would be fun to have a 45/70 GG again.
But I would run a 405 gr @ 1600 fps or less.