I liked this bit of contention. LOL, gotta love it.

"The Marlin Model 1895 .45/70 Guide Gun. You can hunt everything from ratty little deer to Cape buffalo with one, thanks to the astonishing variety of ammunition that’s out there."

I helped a friend with loads for his .45/70 on a Siamese Mauser he had built up in the 70's. At the time I was shooting a VZ34 in .458 2" I had purchased in Smithers, B.C. We used the same loads in the .45/70 that I was using in my .458 2" and received exactly the same vel. likely due to his 24" bl. compared to my 22" one. The slightly larger capacity .45/70 case delivering identical ballistics due to the longer barrel - perhaps. The bottom 3 listed bullets were shot with the same identical load. 68gr. H335 or 56.0gr. IMR4320. I strongly suggest this loads are not usable in a Marlin or any other .45/70 rifle than a Mauser or Ruger #1.
I actually doubt you could get that much of those powders in a case and still deep seat the bullet as is required in a Marlin. Both my rifle and my friend's rifle had fairly long throats. Mine had 3/8" freebore, while his 2/10", thus out OAL was identical.
300gr. 2,450fps.
350gr. 2,300fps.
400gr. 2,150fps.
500gr. 2,060fps.

CAUTION, these are likely 55,000psi or maybe even higher, loads. They were not excessive in the rifles used but would be in a lever rifle.

edited typo, had 3,450fps listed for 300gr.