Been there...most of the lead (not jacketed) loads were for powder I don't happen to have right now.
Good pointer though...that is a handy reference page. I already have it as a favourite.
Thanks anyway.
I presume your 45-70 is of the Marlin variety. If it is, this load, at least, given with 4198 powder, is a very light load.
45-70 385 gr cast; IMR 4198 Start load 23.0 gr - Max 30.0 gr
With 420 grain cast bullets, I use 33 grains of 4198 for a fairly light plinking load. For a heavier load I loaded 43 grains of 4198 with the 420 grain bullet. This was the starting load given in the loading book I had for that load in the Marlin. It was plenty heavy for me, as a few shots made my head ache, but it was actually not a heavy load for the Marlin.
You don't have to stick to certain powders, for certain cast bullets in the 45-70. Of the powders you list, 4756 is for light loads, 4350 is too slow burning to be efficient, but the other three are all well adapted to the 45-70 and cast bullets. The 350 grain bullets you have are pretty light for cast bullets in the 45-70. Mostly they run from 400 to 500 grains.
Thus, you can look at a load for any bullet heavier than your 350 grain, and it would be perfectly safe to use that load with the lighter bullet, as long as it was a suitable load for the heavier bullet.
My criteria in loading the 45-70 is to load up as much as I feel up to in shooting it! I have never come even remotely close to over loading the rifle.