Most seating dies have a crimping groove that can be used to successfully crimp your handloads, even when the cartridge is unusually short. However, the Lee factory Crimp Die depends on standard cartridge lengths with minimal variations to work. I don't know if the shorter Hornady .45/70 brass will work with the LFCD, as I've never tried it.
With a conventional die set (RCBS, Redding, etc) unscrew the bullet seater as far as it will go, then with an empty case on the shell holder, run the ram to the top of its travel and thread the seating die down until you can feel contact with the case. At this point lower the ram slightly and turn the die down another eight of a turn, replace the empty case with a loaded round, and run it up into the die. You should be able to feel the crimp occur. Remove the cartridge and examine the crimp, and adjust the die another sixteenth of a turn up or down to fine tune your crimp, then proceed to crimp the rest of your loaded rounds. If your brass has variations in length, another option is to back off the seating die a few turns, put the loaded round on the ram, run it up, then thread the die down until refusal. Once you get the feel for this, you can make very uniform crimps even when there is significant variations in your cartridge lengths.