Congrats, you have one of the best big game guns anywhere, powerful, flexible, inexpensive. You my want to contact B. Mitchell who has published a journal on top end reloads for the 45/70, and is very knowledgeable on the 45/70.
The 45/70 is also one of the most cast bullet friendly cartridges out there, and I would encourage you to find some good heavy weight cast bullets, made for big game like the WFN or LFN series of bullets. It is with these types of bullets that one can easily create loads much more effective then any factory loads including Buffalo Bore and Garretts as they are bound by legal psi protection b.s.
For pedestrian velocities you can get away with machine hardcast bullets, with "shipping lube" and simple designs like bevel bases, limited lube grooves, etc. If interested in casting your own, LBT, NEI, and Saeco, RCBS, all provide high quality molds in designs that offer good accuracy and top terminal performance, not ease/speed of production and delivery.
With molds as well as bullets, you get what you pay for, so poke around the net, ask questions, most of all enjoy your 45/70, it's the best cal. out there...