In a word - "No".Can a 450 marlin cartridge be shot in a barrel designed for the 45/70 gov?
Being that I've not owned a 450 Marlin, I had to do some research.
1. Never advisable to fire any cartridge in a weapon that wasn't designed specifically for that cartridge.
2. The 45/70 is a straight wall case with a rim. The 450 is a straight wall case without a rim (rimless) and it has a belted case. I seriously doubt that the 450 would even chamber in the 45/70. (don't know for sure, never tried)
3. The 45/70 Marlin max load comes in at slightly over 39,000 CUP where as the 450 Marlin comes in at slightly over 42,000 CUP. This equates to a substantial increase in chamber pressure of the 450 round in a 45/70. Most likely would result in damage to your rifle and injury to anyone in the area.
I highly recommend that you not try this at home - or anywhere else for that matter.
I hope this answers your question.