The cast bullet data is, almost by definition, a reduced load data as lead alloy bullets of a given weight are almost always at lower velo's, thus lower pressures, than jacketed.
In a rifle strong enough for a higher pressure cartridge the reduced cast bullet data of a comparable cartridge wont get you into trouble, regardless of caliber.
IIRC the case capacity of the 450M is so very close to the 45-70 that they are vitual twins, but the 450M was designed to be a higher pressure cartridge from the get-go and avoids the problem of a Level 3 45-70 load finding its way into a Level 1 gun.