I know that the laws are a bit confusing in Indiana about rifle vs pistol rounds. You can shoot the 45/70 in a "pistol" legally.
Here are the eact regs from this years 2012 -2013 booklet.
Legal Handgun:
Handguns, other than muzzleloading, must have a barrel at least 4 inches long and must fire a bullet of .243-inch diameter or larger. The handgun cartridge case, without the bullet, must be at least 1.16 inches long. Full metal-jacketed bullets are not permitted.
Illegal Handgun:
Some handgun cartridges that are illegal for deer hunting are .38 Special, .38 Smith and Wesson, .38 Colt New Police, .38/200,
.38 Long Colt, .38 Super, .38 ACP, .38 Colt Auto, .45 ACP, .45 Automatic and .45 Auto Rim. All .25/.20, .32/.20 and .30 carbine ammunition is prohibited.
Legal Rifle:
Rifles with cartridges that fire a bullet of .357-inch diameter or larger; have a minimum case length of 1.16 inches; and have a maximum case length of 1.8 inches are legal to use only during the deer firearms and special antlerless seasons. Some cartridges legal for deer hunting include the .357 Magnum, .38-.40 Winchester, .41 Magnum, .41 Special, .44 Magnum, .44 Special, .44-.40 Winchester, .45 Colt, .454 Casull, .458 SOCOM, .475 Linebaugh, .480 Ruger, .50 Action Express, .500 S&W, .460 Smith & Wesson, .450 Bushmaster, and .50 Beowulf.
Technically as long as your weapon of choice meets the requirements as outlined above you should be good to go.
Personally I think it really depends on the situation and which DNR officer you get if you get stopped. I think most DNR officers will probably check the headstamp on the cartridge and just go with that. Some might not. Either way I would only be in the woods with a properly headstamped and approved cartridge just to avoid the hassle. Of course you can go into the woods with a 45/70 and cut down brass which in my opinion makes you perfectly legal, but the rookie DNR officer may not think so. Then you have to go through the hassle of proving it instead of shooting game.