It's just one of those things. The 45-70 is a piece of Americana. I recently bought a Marlin 1895GBL myself. Working on a pet load that will push a 405gr cast at 1300-ish fps.I'd say go for it. Upon shooting it you will either love it or not. If not, you can probably move it along for about what you have into it.
I am using 25 grains of AA5744 with my home cast 407 gr (wheel weights - water quenched) and getting very close to 1300. Very accurate even out to 100 yards and beyond. Easy on the shoulder too.
