As long as the cartridge meets the legalities for use on deer in IN (1 set of rules for handgun, another set of rules for rifle), then the platform you launch the projectiles from doesn't matter.
More specifically - I don't know if you'd do any harm to a .45-70 by shooting shortened cases in it or not.
You can certainly get away with it in 357/38 special, 44 mag/44 special, it stands to reason that a .45/70 "special" would be OK. But I don't know for sure.
.45-70 is tapered case, dunno how a shortened version affects accuracy.
Knew some guys at work that did it before the 1.8" change and weren't exactly thrilled. Have not checked back since they upped the length.
Most have gone to .358 WSSM stuff.
This has been my project lately. I'm using a marlin guide gun. I have some 1.8" rounds loaded but have yet to test fire but from what I have read else where they do fairly well.