Seems like we have an epidemic of members looking for reloading data... was there a major book burning I didn't see in the news???
Sorry for the little sarcasm, but you really should investing a good reloading manual and use it. Firearms are very much like people and what one likes another will not. I will not list an exact load as I wouldn't want any one hurt by my miss quote of some data. Typos happen ALL THE TIME, even in those loading manuals. All data should be at the very least DOUBLE checked.
I'll suggest a couple powders, 4198 and RL7 have been good to me, 3031 as already mentioned is a long standing good 45-70 powder.
I prefer to load my handi's 45-70 a bit on the lighter side. So 16-1700fps is my target for the jacketed 400/405gr bullets. In my Rugers, Browning and Marlin's I get that same bullet to 2000fps with excellent results. I do not mean to suggest that the Handi is less capable to withstanding that velocity. To the contrary it is quite a good platform for those loads and many here load it so. I just prefer to keep this lite rifle with a bit less recoil.
CW