I do not think Hornady ever used the LR powder with the LR .45-70. I have never tried to call Hornady and ask because as much as I like the .30-30 LR ammo and I do enjoy the LR powder for .30-30 reloading, I have never had any interest in it for .45-70.
Unless you have information I have not found, you have an unknown powder, in a short case and you are wanting to shoot modified bullets. I recommend against this.
As to Ruger repairing rifles made by JM or REP, I would not hold my breath on that. I doubt that ever happens. I wish I would be wrong on that, but I probably am not.