YES!! You can! I load cast bullets for my 45/70 Ruger No.1, and I have loaded the Lyman .457122HP to 2300 FPS in it using both RE 7 and IMR 3031 with no leading or loss of accuracy. That is a plain-base bullet, and I load it with a Hornady gascheck under the bullet, inverted on top of the powder. For such loads, the base portion of the bullet must be around Brinell 23, and I use LBT Blue lube or the equivalent for velocities much over 2000 FPS.

You can do the same, up to the limits of the Marlin action, and if there is some air space inside the case between the powder chargeand the bullet, just put a .45 cal. Wonder Wad or two on top of the powder charge and the inverted gascheck on top of the top Wonder Wad. The .45/70 is perfect for cast bullets. In fact, there is no reason in the world to use jacketed bullets in a .45/70 for anything at all.