Good morning, welcome and Merry CHRISTmas!!!
There is a wealth of information here on our grand ol' 45/70 gubment!!
As mentioned 4198 is a popular powder. ( it's what I use for my 300 gr handi loads. ) but 3031 is the old stand by. I also load RL7 with 400 gr Speers to 2000fps in my Browning and Marlin rifles. ( the handi handles these loads fine, just my shoulder objects)
For an excellent lead bullet load look at XMP 5744 powder. It's a newer powder designed expressly for lead bullets. It works very well in cavernous casings like the 45x 70,90,100,120 as well as the 50x70,90,100,120.
I have a Couple of molds I like. One is an old H&G 450ish spritzer and another is a flat nose 420grs of coarse this varies with your lead mix. Both shoot very well, although I haven't shot any gamewith either.
Good luck with yours. It's a favorite here and for very good reason it's a grand old caliber!!
Happy holidays,
CW