Hi Dave
All loads listed in the replies look safe, and reasonable. I will not claim to be an expert re-loader, or to know it all, anyone claiming that should be avoided. (I'll explain that another day) I do have 25+ years at the reloading bench and have been working with .45-70 since 2004 in the Handi Rifle.
There are many loads that work well in the Handi. Your best bet for low recoil is lighter bullet weights. In mine 405 gr cast shot best, out to 125 yards, 500 gr cast bullets while slow are fun to target shoot with out around 250 yards, and beyond. (Some shoot 1,000 yards with 45-70 and 500+ gr bullets and black powder) For hunting deer, the 300 to 350 ish gr bullets kill quicker than the 400 and 405 grainers. (not just my opinion others have found this to be true as well) For boar and animals with thicker skin, and heavier bone than whitetail deer move up to the 400 grain bullets. 300 grain bullets over 63 gr of 3F black powder (goex) kicked more than any mule ever could, smokeless loads are alot tamer. I do not use pistol, or shotgun powder, the 45-70 case is just too big for those powders, and there have been many documented cases of using too little of too fast of a powder causing damage to chambers of some very strong rifles, and frame ruptures of some lever action rifles. Many people fire many hundreds of loads using these powders, with no ill effects.
My favorite powder for the 45-70 is IMR 3031. With this powder your shoulder will make you stop long before the pressures cause you to stop increasing the powder charge. Get a good loading manual, and one of the caliber specific booklets from Midwayusa, or cabela's.
Oh and one more thing, have fun!!